Their Own Worst Enemy
It's like running an app that asks you to disable your firewall; that app is never run again. Please disable my ad blocker? Sure, if you stop pushing turds through my digital letterbox.
It's not so much the addition of an advert to a video you want to watch, it's the increasing number of adverts rammed into the videos. Time was when you'd have an ad you could skip past after 5 seconds at the start of the video, but now it seems to be two adverts to start with and a load more throughout the video which just get in the way, which is why people started using ad blockers.
YouTube (and others) need to rethink their whole strategy on this and be sensible: I'm not averse to a subscription model for a service I use but it's the cost that dictates whether I use it, and these companies seem to think that $10/£10 (or more) a month is a reasonable entry price. It isn't, it is way too much and could easily be half or a quarter of that while still allowing them to make a profit. I would happily pay $2.50/£2.50 a month for YouTube to be ad free and would allow it through my ad blocker, but unfortunately the corporate greed with these companies is so rampant they wouldn't go for such a low subscription price which is a shame as the cost to set up and collect a subscription is exactly the same. What do you want: A minority paying a high subscription fee whilst also having to try and block millions of machines using and blockers to avoid embedded adverts, or a majority of reasonably happy subscribers paying a dirt cheap subscription each month? Or I'll put it another way: $2.50/£2.50 a month every month for a few million subscribers for potentially years, is much more that $0/£0 a month from no-one.