It's not cleaning up it's image out of some sort of moral epiphany. It's purely about profits and greed. They built their business on sex workers and made a fortune, but now they want to cash-in even more by going public. This requires getting out of adult content and completely messing over everyone they built their business on.
In the end this is going to go down as a colossal mistake and like a 101 lesson on how to destroy your own successful business. Ideally all OF content creators find another platform that allows them to continue and it becomes hugely successful. As for OF, inevitably they'll be left with near-zero content creators and few customers, which seems fitting. There are already other better platforms for PG content or for fully pornographic content, so I'm not sure what market OF thinks they'll be left with. OF had a successful niche and just threw it away.
Blizzard did the same in about 2010 when they took wow and casualized it being greedy and hoping to turn their 12M subs into 20M. Instead they turned it into 5M, and probably closer to 1M now.