It's the players, there's obviously a rotten core that's now gotten 2 managers sacked and about to get rid of the 3rd. They can play when they want to, but they don't want to most of the time.
Yet the players won things, and Real have 'gotten managers fired' yet won back to back to back CL titles as well. So maybe, just maybe, the managers were failing and the players are rightly not putting up with it and managers are getting fired for not being good enough. Apparently it's fine that if a player isn't cutting it a manager cuts and then sells them, but if the manager isn't cutting it and their system doesn't work, their training is awful and they **** off everyone at the club it's everyone else's fault.
For no apparent reason at all fans seem to love managers and blame players.
Personally I think there are times where a managers ideas work great with a very specific set of players at a very specific club and in a specific league, the manager believes it's entirely them and every single thing they do is crucial to this. So they go somewhere else and assume if they do the exact same things, same training, bring in one of the same players, maybe two, if they tell the players the same things and play the same way they'll get the exact same result.
The best managers adapt as much to their players, a league and a situation as they expect players to adapt to them and they keep adapting over their career. Other managers think this worked in situation A so if I keep doing the same thing it must work in situation B. I think this is what you've got with Sarri, a guy who is stuck rigidly to trying to recreate what happened with Napoli and is utterly unwilling to adapt or think outside the box at all.