Tim Burton recently

Burton has lost his way. They're probably better off without each other.

Tim finds new muse: Eva Green.

I strongly suspect that Burton's relationship with Depp was like Scorcese's relationship with DeCaprio… it was based on the actor's ability to get films greenlit.

Depp is no longer a box-office draw, or someone the movie studios want to invest in.

Willy Wonka.

Depp was pretty much cancelled after the Heard allegations. Other than Fantastic Beasts he hasn't gotten a part in a big budget, mainstream American movie, and the people who made that movie were attacked by certain people and the media for doing that. Other than that's been indie movies for Depp the last three years or so.

Because Dark Shadows (2012) failed.

Burton and Depp have kept going on the fumes from their "Ed Wood" glory days for awhile with increasingly bad movie after bad movie. I think they just finally used it up.