People were okay with ads, then YouTube started making them obnoxious. Ads every 2 minutes, postroll ads that interfere with autoplay, incredibly long "ads" which mean you need to watch YouTube like a hawk to make sure your 5 minute video hasn't been interrupted by an hour long ad you need to manually skip.
There's a balance that people need to be happy with a service, and if the service doesn't provide that then people will use things like adblockers to get it themselves. It's the same thing that happened with the first "adpocalypse" that brought about most of the big name adblockers in the first place: people were okay with unobtrusive ads, then advertisers started running popups, overlays, autoplay videos, fake system notifications, on and on and on. The advertising became so disruptive people were unable to use sites without adblockers. And so the cycle repeats.