I suspect (and this is really, nothing but speculation based on some whispering that are hardly of ironclad credibility) that Derrickson wanted to lean more into Madness part and Feige more into the Multiverse part (as in, highly interconnected "event" solo movie that ties into WV, Loki, future movies, future shows, introduces new characters, etc).
If so, if you were looking forward to DS2 because of the "MCU's first scary movie" talk, this might be bad news for you.
I was looking forward to DS2 as a highly-interconnected event movie, and after thinking about things a bit more (and pending the identity of the replacement) I am pleased as punch.