My bet is they're trying to follow America's lead. Their national interests seem relatively delineated, and bitcoin isn't really in that set. When they banned it in the past, it looked likely that America would ban it. But now America is turning friendly to bitcoin, so China might think there's more to gain by following that lead.

Also a ban in China is nowhere near as total as a ban in the west. Like, while I was there, they would periodically send out police to all the bars and restaurants that foreigners liked and shut them down, and it was terrible for like two weeks, and then they forgot about it and the exact same businesses just reopened with no issues. Like twice a year. I think they just don't see the law as a set in stone kind of thing.