It's not often that respectable starting quarterbacks make it to NFL free agency.
It's especially rare when it happens without extenuating circumstances. Drew Brees bolted from the Chargers after the team used a first-round pick on Philip Rivers. The entire NFL was concerned with the state of Brees' throwing shoulder at the time; it was the reason the Dolphins avoided signing him. When Peyton Manning hit free agency, it was because he had missed a whole season following neck surgery, and the Colts were able to use the No. 1 overall pick on Andrew Luck.
Cousins isn't as good as Brees and Manning were at their peaks, but he is able to say that he's hitting the open market injury-free. Cousins is one year removed from a season with a healthy Jordan Reed, DeSean Jackson and Pierre Garcon in which he finished fifth in Football Outsiders' passing DVOA and sixth in Total QBR. While he had more mediocre numbers last season -- 18th in DVOA, 15th in QBR -- it's not hard to argue that Cousins is one of the top 15 quarterbacks in the league. He's certainly in the top 20.
Washington moved on by acquiring Alex Smith for a third-round pick and cornerback Kendall Fuller. With Jimmy Garoppolo's new contract setting the bar high, you'll forgive Cousins' agent, Mike McCartney, for being gleeful about the concept of his free agency.
As of this past weekend, we learned that Cousins is down to a final four, but there are two teams that need him more than anyone else.