Most importantly because I don’t want to support that wholly unethical company that google is, and I think nobody else should. They already have plenty of money, which would be enough, if they wouldn’t be a publicly traded company with endless thirst for more and more and more and more.
Ads are not just inconvenient but very often annoying and misleading, so I can’t blame anyone for that.
Micropayment donations might, though. It’s not annoying, not misleading, and there is a considerable amount of people even now that regularly donate/otherwise support their favorite content creators, and this would be even more convenient because it is automatic and the amount depends on how much time did you watch videos.
And it doesn’t even necessarily depend on cryptocurrencies.