The thing I think sets QBs apart specifically is you could make a strong argument that taking less to have a better team around them can pay off financially in the long run. Purdy is a marketable guy. Being part of a winner, even if it means less NFL salary wise, is a smart play. He's proven he can get the job done with talent around him.And guys take heat from the players union and other guys if they start taking less than market value to help the team. Brady could do it, but not too many other guys could get away with the home town discount stuff.
There are a ton of down to earth good dudes playing in the NFL, and a lot of them say all the right things, and have nothing but good things said about them. And they pretty much all take as much as they can get.