From what I've heard, they didn't do Age of Sigmar because of the rules or whatever, they did it so they could render pretty much every old figurine obsolete and get people to buy the new ones. Since the universe had stalled for a while, people were using their old gen figurine for whatever unit and heroes that never got changed(like mannfred, karl franz and so on) instead of buying the new ones. But by basically killing everybody but a few people and merging armies together giving them new appearance, banners and whatever the fuck, anyone who wants to play Age of Sigmar kinda has to rebuy most of their armies.
They're apparently doing pretty fucking poorly, which is a large reason why they've been selling their IPs to everyone who wants it now, while say 10years ago, they were very particular about the games being made with WH Fantasy and WH40K IPs. That's why there's like a dozen of warhammer games coming out lately/soonish.