Considering everything DC did to sway Bendis to there side (AFTER CWII), proves that that doesn't matter. Direct sales may not be ""the best"" (whatever that definition may be), but when he's still producing what many people consider to be quality content, then a recognizable and popularl name is something that's still valuable.
Mister Miracle still sold very well considering the property and what the book actually was, that was sold pretty much entirely on King and Gerads name. And you forget that the trades have been selling like gangbusters. They released like three different versions of it within the span of a couple months, that should tell you how well it is doing for them (it's almost like the direct market isn't the be all end all for success
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And I'm basing his popularity off critical acclaim and fan response. HiC is his only true dud, and even then its got some fans. Despite what you insist, if you actually look around the internet, his Batman tends to swing more positively than negatively, and everything else (Vision, Sheriff Of Babylon, Mister Miracle, etc.) have received near universal praise. And then you can just look at his presence on social media, and see the amount of people that love him as a person, and just how many industry people (writers, artists, etc.) also love him too.
It's called common sense. He gets hired to write the movie at the same time as his removal, we all know this isn't a coincidence at all. So that's where the speculation comes in, and using actual logic, it's not hard to deduce the possibility that is directly what resulted in the book change. There's actual evidence to back up this speculation, whereas yours is literally just believing unconfirmed gossip.