the excessive spin-offs
Honestly I think there's a few main reasons for it. It's not that WD is so popular as it isn't anymore. But it still has potential. Because possible zombie stories are endless. And with ending the parent show, they do away with any last vestige of pressure of being beholden to the original source material. I know they were always loose with it anyway, but now it all gets to be their own thing completely. A whole new world... beyond, if you will ;)
I'd actually really respect it if all the spin-offs weren't happening and their announcements were red herrings to lull us into a false sense of security and be more surprised.
But I doubt it. They insist on making the franchise live up to its name.