He doesn't have to. Nothing says that Philbin has a zero tolerance policy. Johnson basically came here with two strikes already and to my knowledge Amaya was strike free.
Nor do you have to be constant with your stars and backups.
If you got a third stringer that fucks up -- get rid of them there are plenty of guys just as good as him who can keep their nose clean and are willing to do whatever it takes for a shot in the NFL. If you got an all-pro player that fucks up, but even with his off field fuck ups, is constantly a significant reason for team wins, you do your best to get him on the straight and narrow, but you don't get rid of him.