In fairness to Google, costs to host video would scale with viewers. Unless creators are willing to pay increasingly excessive costs as their viewerbass grows (which I doubt) some kind of per-viewer cost (like ads) needs to be charged.

There's no guarantee creators can collect as much income without Google either. Google has proven they can get way more income from ads than pretty much everyone else, and even bug channels with sponsorships still derive a very large income portion from Google ads (based on what I've heard from LinusTechTips videos)