I don't know, at some point, you have more money than you can ever possibly spend, so what's another $25M going to do? There are plenty of rich actors who turn down big-money roles for stuff that's more artistically fulfilling.
That's assuming they got into acting for the art of it though.
I have no clue about how much money he has, other than the new million per episode deal. So he may not be totally set for life yet. (Might be bad with money + agent + manager + taxes + houses + cars + family + moochers + lawyers) Also that kind of fame and money changes people. He may have been cool with doing small things, but maybe he isn't now that he's on this success wave?
Also, Zach Braff. Do we really want another Zach Braff running around?