I'm no developer* but my wild-eyed conspiracy theory about the unity stuff is that it's about data harvesting bullshit. They merged with an adtech company last year, right? What better way to distribute that shit than to tuck it into the runtime code that accompanies every Unity game, potentially in a way that circumvents apple's anti-adtech stuff. The fee itself is maximizing return by getting a cut from big f2p games; indie developers that get fucked by it are just catching shots because they're too small time for Unity to care about.
*My background in accounting could argue that I'm trained to be a business asshole, though.