So, when will they move from big tech platforms to better alternatives like the fediverse?

That would be better long term as corporations will always do what is best for their shareholders and bottom line. It would be best to direct their energy into destroying them by moving away from them and into something they truly have control over.

Let the big tech suffer and become dumpster fires meaning no one will want to use them.

I do feel sorry for them, but there are better solutions, though I wish them luck in their efforts.