Might be he got fired and he decided to do this as a "f--k you" on the way out. That I can respect, in theory.
With the way MCU does things and all their composites and so on, Feige and others can literally remake the movie any time during post.Anyone remember how pissed Spielberg was about the “dancing Russian” in ‘Kingdom of the Crystal Skull’ leaking plot details, that he removed his entire scene?
This trailer leak is just nothing to look at with all this bizarre CGI crap.
Mostly though it does seem a lot of the press hoopla about multiverse was accurate after all.