Mixture of everything i'd say
Bartra hasn't been the same ever since the terror attempt, which is part of the reason why he's gone imo.
Watzke definitely didn't make the best choices regarding coaches and he's getting a fair share of criticism recently, and rightly so.
Fans pretty much made their piece with losing their best players, since they know they can't compete financially, and whilst it is a decent team, it's nothing like what it's used to be. Probably cause you can't always bet on finding a worldclass talent to replace a star player, that can't work out every single time. It's been a constant watering down of the squad

shifty
I kinda hope RB takes their spot as #2 in germany, mainly because of how the Dortmund fans behave towards them. And because of Ralf Rangnick, guy is a genious.