Because it provides me with value that imho justifies the cost in addition to supporting creators more than what they would usually get from me consuming their content.

Realistically, 50% of the videos I watch are random creators I don't subscribe to and I would not make the effort to donate to just for watching one or two videos. These people still worked for that content and deserve payment.

I could install an ad blocker and basically fuck them over for using YouTube as their platform, or I can pay money, have no ads and support them.

I think that's a more ethical thing to do then to pretend that they don't deserve compensation because realistically, they have no alternative platform that generates them enough money to continue what they are doing.

Nobody can make a living on peer tube or any of the other alternatives, except for maybe meta or TikTok but they are far worse.