Why are American women more successful in tennis than U.S. men?

What does the future hold for men's and women's tennis? (1:31)

John and Patrick McEnroe look ahead to what the next few years of tennis could look like, following the conclusion of the US Open 2019. (1:31)

NEW YORK -- The spotlight on American women at the US Open this year was relentless, shifting from 15-year-old sensation Coco Gauff to 37-year-old Serena Williams to iconoclastic stylist Taylor Townsend, pausing now and then to give us a glimpse of a Madison Keys, Sofia Kenin or Caty McNally.

Lurking in the background, out of the light: an embattled generation of American men.

As fans cry for the next great American male champion, the current veterans -- including John Isner, Sam Querrey and Steve Johnson -- are still oppressed by the Big Three. Meanwhile, a cohort of talented youngsters are doggedly trying to move up from the Top 50 into the spotlight. But the slogging has been slow.

The U.S. had four women in the US Open fourth round, led by finalist Williams. Three women from the U.S. were ranked in the top 10 (Williams, Keys, Sloane Stephens) during the Open, another was in the top 20 (Kenin), three more ranked No. 36 or better -- a grand total of 13 in the top 100 -- and, of course, Gauff. Other talented players wait in the wings.

The men?

Not a single American man survived the third round. They have nine in the top 100, but none ranks higher than No. 20 Isner, the only one in the top 25. Three 21-year-olds (Reilly Opelka, Taylor Fritz and Frances Tiafoe) are in the top 50, led by No. 30 Fritz. But there's no male franchise player like Williams, or a surefire future one like Gauff and not a single active singles Grand Slam champion (the women have three).

There are powerful reasons for the disparity, and most of them have little to do with the quality of the heavily-funded USTA training programs, which allocate resources equally to the men's and women's programs.

Patrick Mouratoglou, Williams' coach and operator of the eponymous academy where Gauff and men's star Stefanos Tsitsipas have trained, told ESPN.com: "I can't comment on what the USTA is doing, but something more general applies. When you have a star in any sport in any country, the kids want to be like him or her. And the U.S. doesn't have a male tennis star who can compare with Serena and Venus Williams."

Timea Babos, one of the top two-way players (singles and doubles) in the WTA, knows the value of having a domestic role model, as she didn't have one growing up in Hungary.

"It's important to have these great idols," she said in an interview. "We never had such players like the Williams sisters. I looked up to (Russia's) Elena Dementieva, but that as personal. Having someone from your country at the top creates a lot more interest."

Call it the "Williams Effect." It is powerful, difficult to quantify and unique. It has drawn in volumes of gifted players, particularly people of color, and in a manner and for reasons that reach far simply for having two great champions as high-profile role models. Colette Lewis, the doyen of junior tennis and author of a blog and the @zootennis Twitter feed, told ESPN.com:

"You can't forget the impact of Richard [Williams, the father of the sisters]. A lot of African-American men looked at Richard as their role model, instead of their kids just looking up to Venus or Serena. Richard was basically saying, 'You don't have to come from a lot of knowledge of this, you can do it on your own. It inspired a lot of parents (including the Gauffs)."

In his autobiography, Richard Williams wrote about the moment the light bulb went on over his head. Channel surfing at home, he happened to catch the presentation ceremony in which then-25-year-old pro Virginia Ruzici received a prize-money check for $40,000. Stunned by the payoff for a few hours' work, he almost immediately resolved, "I'm going to have two kids and put them in tennis."

That's just one of the ways money has been a critical driver in tennis' ability to recruit the best female athletes. Insurgents in the ATP are busy kicking up a fuss about how little lower-ranked tour-level players compared to their counterparts in more popular sports like basketball or football. For women, though, tennis offers the biggest payout of any pro sport -- by far. Eight of the top earners in women's sports last year, according to Forbes, were tennis players.

Successful Olympic stars and others (such as top 10 earner Danica Patrick) can also capitalize in the marketplace, but as Lewis said: "The Olympic sports and World Cups that everyone watches occur every four years. You can become famous, but then it fades. A tennis player has four chances (the Grand Slam tournaments) every year to be famous, to make money (including endorsements) and stay in the public eye."

On a more modest scale, the promise of a potential college scholarship is alluring to many parents. It's a fallback in case the child is an excellent player, but not pro material at a young age. That option is open to men, too, but with fewer scholarships available.

According to Kathy Rinaldi, the head of women's tennis for the USTA, "It all starts with a broad base, and it narrows as you go up. The women do mature earlier, so they tend to stay in the game if they experience some success."

Martin Blackman, general manager of player development for the USTA, told ESPN.com: "It's a value proposition when a parent is choosing a sport for a child. Fully funded Division I colleges have eight full scholarships to offer girls, compared to four-and-a-half for boys (The discrepancy is meant to restore the imbalance created by the abundance of scholarships given to men in sports like football)."

The scholarship pitch brings many gifted female athletes into the USTA fold at an early age, and there's little to lure them away. It's different for young men. Although there is no hard and fast data, tennis ranks somewhere in the bottom half of the 10 most popular sports on most lists. It's no secret the popularity of the game has exploded worldwide, ending the reign of the two longtime superpowers, Australia and the U.S. But it also turns out that many other nations have a built-in advantage in recruiting talent.

"In Europe, tennis is No. 2 after soccer," said Mouratoglou, who currently has no promising players from the U.S. at his academy in France. Mouratoglou believes boys in Europe can grow up wanting the be the next Gael Monfils or Rafa Nadal. But in the U.S, "You could have another Roger Federer and probably he still will not be as popular as LeBron James."

Despite the enormous population advantage enjoyed by the U.S., the base of elite athletes is limited. In the halls of American high schools, the heroes are the quarterback and the shooting guard, not the kid ranked No. 3 in some regional, extra-scholastic organization. There's no homecoming celebration for the tennis team.

Rinaldi is sympathetic to the plight of her male counterpart (Kent Kinnear), and suggests the outlook isn't as grim as some claim. "The men have a different pathway, you have to look at that," she told ESPN.com. "Our guys are stepping up." She said she expects "great things" from 21-year-olds Fritz (ranked No. 30), Tiafoe (No. 43) and Opelka (No. 46).

"When you look at how the longevity has increased," Rinaldi added. "You can see that time is on their side."

Blackman is committed to overcoming the obstacles faced by the U.S. men and the perils associated with such attempts. He said, "A lot of the challenges are structural, or could be perceived as external (the popularity of other sports), but we have to tackle them. We have to do it, and we're going to do it without lowering the bar."

To that end, the USTA has launched the "Net Generation" campaign, an initiative to recruit talented athletes and keep them satisfied with the tennis experience. By the start of 2021, Blackman said, the USTA hopes to roll out comprehensive "format reform." That will include a perhaps dramatic shift to team play, because research has shown that young men much prefer it to the sometimes lonely experience of an individual sport.

Blackman insists the benchmarks for success will remain rigorous. Right now, the first target for players in the player development program is a top 20 ranking. The next box to tick is top 10. After that, elite players tend to build their own teams and federation support dwindles.

"Understand, there is a real sense of urgency regarding the men's side," Blackman said. "We have three young guys in the top 50. It's the first time in a long while that we've had that."

That may not be so impressive when compared to the U.S. women, but it's a start.