How would you pretend to show the adverts in way that's undetectable? Even if you had complete control of the browser through your ad blocking extension (you don't). Youtube could trivially get around this by not sending the actual video content down to the browser until after the expected length of an the ad.
Like the ones for Spotify that would set your system volume to 1% when it detected an advert playing.
For video content an alternative would be to replace ads with a clip from the next video on your playlist/suggestions as a short "coming up next" preview.
IIRC there was a recent Android compromise that played ads under the main window, invisible to the user (except for performance and battery drain) and collecting $$$ for the company that sold the ads.
How would you pretend to show the adverts in way that's undetectable? Even if you had complete control of the browser through your ad blocking extension (you don't). Youtube could trivially get around this by not sending the actual video content down to the browser until after the expected length of an the ad.