Because the ad is delivered in one, and not in the other.
You're comparing two unlike things. The equivalent to leaving the room during TV ads would be leaving the room during YouTube ads (or changing windows/apps).
I am talking about not watching YouTube ads. Not comparing TV to YouTubre. As I asked another poster, is there also an obligation to buy the advertised product? After all, if no one acts on the ads the advertising will eventually stop.
You're comparing two unlike things. The equivalent to leaving the room during TV ads would be leaving the room during YouTube ads (or changing windows/apps).