Amazon Prime has ads by default now, or you can get rid of the ads if you pay an additional $3 a month.
If they start showing some amount of ads on my YouTube Premium, and start charging a fee to get rid of all of them, I think it will just piss me off; I already pay for YouTube Premium, I am not going to pay extra for extra ad free.
You can either reduce the product or increase prices, or both if you're really going for it.
It is simply a change in price, dressed up to be more palatable for people who are not as discerning.
Before, Amazon Prime Video without ads was the price of Amazon Prime. Then it became the price of Amazon Prime plus $3 per month. Now it's the price of Amazon Prime plus $5 per month or $46 per year.
Same thing with Youtube, or any other product/service, price changes happen all the time. Pay if it is worth it, or don't if it's no longer worth it.
I've grown kind of tired of YouTube as of late anyway, and it's not like I get a lot out of it in any kind of deep meaningful sense. I probably could fairly easily justify canceling it and surviving on my blu-rays.