Though I do suspect I'm in the minority on this website, £12.99 a month (£155.88 a year) for one website is very hard to justify when you're on very little income.
They are positioning YouTube as a super-premium product (relative to other streaming services). An underlying takeaway might be that advertisers no longer value users "on very little income" in a positive real-rate environment.
(I'd prefer if YT would prevent creators for advertising in Premium videos, but I bet that would not be accepted happily either.)
...alongside advertisements. They do get a share.
I don't think most people who use ad blockers understand that the ads are literally the price you pay for the service. If you think your time is worth more than the ad length, work for an hour and pay the subscription. I know it sounds crazy when I put it this way, but there's no such thing as free internet video.
Edit for the angry down voting hackers: Try searching YouTube next time you have a problem with your vehicle or household appliance. There is usually somebody there who made a video showing you exactly how to fix it by yourself, so you don't have to buy a new one or pay somebody to fix it. There is no better resource AFAIK.