What evidence do you have that most creators have sponsors?

All the Youtubers I am subscribed to have sponsors which is arguably not a representative sample size but still means that I can feel good about blocking YouTube's terrible ads on their videos.

Most don't but bigger channels would. You may only subscribe to bigger channels.

I would say that it's fair to call them bigger channels (as they are not niche 50k subscribers ones), but I think you'd still be surprised by their size, some more technical ones will have sponsorships by Chinese electronics makers (JLC PCB, taobao, banggood, etc...) while being at around 300k subscribers which is not that much in the modern YouTube.

Most is too strong, but a fair number of the ones I watch do. The creator is upfront about the sponsorship so it is clear. Generally this means a big announcement and then future videos show the product. Wd40 sponsors several that I watch, and following the sponsorship the channel was careful to point out they were using Wd40 for whatever. (in most cases the video would have been about them using something before like wd40 before the sponsorship, but the what may have been hard to tell)