Isn't it the coach's job to work with players so that they come to work with great attitude?
What's he supposed to do? Sleep over at a malcontent's house, and gently wake him up in the morning by saying "Wake up, Sleepyhead?" Then he can make a breakfast of scrambled eggs, pack a lunch in a Boston Celtics lunchbox, and drive him to practice so the player doesn't have to deal with Boston traffic and roads?
The vast majority of players seem to respect both Stevens as a coach as well as the culture he's instilled within the team. If he doesn't want to deal with the minority of players who won't buy in, that's being a good coach for the other 14 guys in the locker room.