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)
The cost to serve the video file is much lower than what Google says it costs. Moving a terabyte of data is quite cheap to do, yet GCP, AWS and ilk continue to have eye-wateringly high data usage pricing.
If a video goes viral and you shoot past that you'll probably get a call from them.
You also have a finite amount of storage space available with them, which depends on the account tier you're at: no infinite storage like with Youtube. (And with 4K video nowadays, that can be burned through quickly.)
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)