The sheer amount of ads on youtube is what's making people use ad blockers. Two unskippable 15 second ads after one minute of a ten minute video is ridiculous.
Honestly that's the uploader's fault. They're too lazy to manage their ad locations and let Google do it for them. Google always adds way too many. I make sure my videos never have more than 3 in 30 minutes, and I craft the videos so that they have precise break points like old school television. You'll (almost) never see an ad on my videos that interrupts something important. It takes so little effort to do this.
I think they've been A-B testing and slowly moving more people into the "disable your adblocker" group to see how it goes. You might be one of the lucky ones who haven't been pestered yet. I have one low usage (if that's relevant) account that hasn't been warned yet. Proofreading edit: See below.
My main account got the warning a while back, and I thought I was getting away with it until they did a whole "you get three more videos and then we're blocking you" and things became somewhat more difficult to work around after the third one.
Of course, they don't seem to have started counter-blocking people who aren't logged in to their platform (admittedly this conclusion isn't based on much. It worked for me and I've seen at least one other comment online that implied it also worked for them), so an incognito/private window might work if you really need to watch that one video.
Proofreading edit: My memory is faulty and the account referenced in the struck-out sentence might not have been logged in for a while. It was logged out when I checked and I remember deleting cookies some time ago. Logging into it reminds me that they won't even show suggestions to logged in accounts if they have their Watch history disabled.
Seems like their current model is to lure people in with (subjectively) entertaining videos, presumably convincing viewers to create an account and/or log in so that they can comment on videos, etc., and in return YT get lots of lovely ad views and targetad adalytics.
It will be interesting to see if they take another leaf out of Elon's book and make the whole site login only. That would be monumentally stupid, of course, but money.