"We look like a team that is firmly committed to being mediocre," Van Gundy said.
The Pistons fell to 23-20 and are in sixth place in the Eastern Conference.
Van Gundy called the Pistons' first-half effort "deplorable," adding that he was disappointed to see his team constantly come out flat on the heels of encouraging victories like the one the Pistons had Wednesday in Houston.
"In the first half, we played nine guys. I thought one guy put out a good effort defensively," Van Gundy said. "Aron Baynes tried hard, and I thought the other eight guys virtually put nothing into it on anything."
Detroit was down 72-53 at halftime and didn't get closer than nine points the rest of the way.
The Pistons did show signs of life when Jennings hit a 3, a 9-foot step-back shot, a driving layup and a couple of free throws during a 19-2 run spanning from late in the third quarter to early in the fourth. Stanley Johnson's layup capped the run and pulled the Pistons to 90-81. However, they couldn't sustain it.
Jennings pointed the finger at himself and fellow point guard Reggie Jackson for a lack of leadership.
"It has to start from the point guards, from me and Reggie," Jennings said, according to the Detroit Free Press. "We're the ones controlling everything and doing everything on the court, and we have the ball in our hands 90 percent of the time, so it definitely has to come from us."
Jennings also said the players need to do more to "police" themselves.
"You gotta challenge your teammates," he said, according to the Free Press. "This is a big boys league, so you can't get in your feelings.
"Guy says something, say something back, squash it up and let's go. I just think that's healthy. Great teams in the league have confrontation. They have guys talking."
Forward Marcus Morris backed Van Gundy and Jennings.
"We are coming out with no energy," he told the Free Press. "Everybody has to hold each other accountable. We come out and aren't playing hard on both sides of the ball. After a while, it gets real old."
The Associated Press contributed to this report.