Bit of both, but mostly... Magic was an egomaniac drug addict and Westhead was a not very good coach who was handed the best team in the league, and was on the brink of firing anyway.
The problem is, everyone is acting like it's straightforward. If players tune out their coach they are not doing their job, at least as much if not more than the coach.
If they are bad players and the coach has been a good coach you dump the players. If they are good players, you dump the coach because good players are more valuable than good coaches.
Sometimes it is clearly on the coach too, like late era Jerry Sloan, he just wasn't interested in making an effort anymore. Sometimes the problem is just a bad match between player and coach, sometimes the player is just a malcontent.
The key is figuring out which it is. However... most times it's neither, it's just a stretch of bad performance. And sometimes it's just a situation where your best players aren't forceful personalities and shaking up the situation with new supporting cast can get the best out of coach and player. Like Ricky Davis, when he tunes out the coach you get rid of him, because that's who he is, he's a not that good player who doesn't like having any coach. If LeBron wants a change you do it, because LeBron is an elite player, and as an added benefit, he isn't going to quit on your team.