YouTube is renting out billboards at a music festival, and the advertisers, predictably, want to know who's playing. "Well, I dunno, like, whoever shows up" has proven to be an answer that they can't get away with. YouTube's negotiating position with advertisers depends on how they can position their package of advertising space. Right now they're trying to sell a big bundle of uncertain providence, with loads of little no-namers mixed in with the heavy hitters.
But what can YouTube do? If they split it up, they now have a gold package, a silver package, and a shit package. The rates for the shit package would be so bad that current YouTube revenue starts to look like winning the lottery. The smallest channels are subsidised by the bigger ones, not in terms of views but in terms of reputation. So if you need to improve the reputation of the group, what's left to do but drop the weakest performers?
If you're thinking "but that's totally illogical! Smaller channels collectively contribute an enormous number of very valuable advertising impressions", you're right, but making the same mistake YouTube did. The advertising industry isn't logical, it's 18 layers of ticket-clippers and con men playing telephone with money. It doesn't run on economically rational real-time bidding systems, it runs on trend-chasing and reputation. That other stuff is just to keep the nerds happy.
So, like in every other field Goophabet has entered, the techno-utopianism lasts right up until it hits the balance sheet. Party's over, folks. YouTube is an advertising company and now it's realising it has to act like one.