Not only is PixelFed not a competitor in terms of users, but the dev is desperate to cooperate and welcome Meta to the Fediverse. So it doesn’t represent any kind of threat for the company’s goals, at least at the moment.
See how quick he was in defending meta after they came with the bug excuse and how quickly he’s adding threads to the fediverse datebase to the point that the clone of Zuckerberg’s account that cannot even fully interact yet is called “the most popular fediverse account”
Well, it’s a list of "well maintained/moderated servers
Any server that federates with threads, a product of Meta a company known for their low quality moderation and lack of ethics, is clearly not a well maintained/moderated one.
It’s not a new rule. The admin is just applying the sites rules as they are, instead of making exception for threads as many of the techbro admins that are getting their servers excluded have been doing.