Earlier quoted context omitted.
I suspect they're going to soon do what Amazon did as well, where they start putting ads into the regular YouTube Premium service, and charge an extra $3 a month for a completely ad free experience. I have the family plan shared across six accounts, and it went to $26, which really isn't that much but I'm not entirely sure why they're doing it.
This has happened to me btw. I can only suspect they are "testing" the reception.
I can't speak for anyone else, but I have a very strong, borderline-irrational distaste for ads. I hate advertising, I hate having to watch advertisements, I will go out of my way considerably to avoid ads. I have over 400 blu-rays specifically because I wanted to guarantee that I don't have to risk seeing ads in my media.
I liked YouTube Premium because it was an ethical way to avoid ads on YouTube; there's always been adblock but I always felt bad depriving creators of their revenue; most of them (at least at the time) weren't big heartless corporations, they were individuals creating stuff.
If I start seeing ads unless I'm extorted for more money, that might end up being a final straw for me.