My brother in Christ, being watched is the goal of any content creator, that’s unrelated to advertisements. Now Youtube ads are paid (lets simplify a bit) blindly once you click the video, it’s a metric, you see those if you want access to the video.
If the content of the video has the guy saying “thanks xyz for sponsoring this raid shadow legends” that’s a contract between the guy doing the video and the sponsor, following metrics agreed between themselves, it has no ties with “the purpose of youtube” simply because… it’s not youtube.
Will there be people doing cheap content to get “easy” sponsor money? Sure but if the content suck you won’t watch it. It’s a loss just like if the motetization was following any other driver (as long as the driver is… watching the thing rather than not).