Kindle Create was glitchy on my computer and didn't create that nice of a book. I was happy to get it off.
This is a stupid rule. They're pushing people into going wide, and D2D's formatter is much nicer, does more, looks better, and still gives you a .mobi. Also, wide, you're going to have a better chance of getting Bookbubs, and they're hundreds of times more effective than Amazon Ads. So if this is their aim, to make more people jump to wide, congrats Amazon. Ooops, that was not your aim? Change your approach.
This is what happens with behemoths. They think they're so important, they can screw everyone every which way, they don't listen, and they don't care, their cutting corners to drive up quarterly earnings means a worse experience for everyone...which leaves more openings for other, more flexible companies to step in. Trade publishing suffered this way because of Amazon, and Amazon will suffer because they are now the un-turnable Titanic, stubbornly heading toward the iceberg.
I'm looking forward to the next innovation, the next publishing system that undercuts Amazon. This time, I'll be a very early adopter.