They prefer you use youtube ad-free than go take the crowd to another platform.
Microsoft famously said that they prefer people to pirate Windows than to use Linux/Mac.
This leads to an Apple situation where Apple doesn't have the most users but most of the money goes to them since they can extract much more money per user. It isn't a bad situation to be in.
Of course Vimeo would have to fight off adblockers too to compete in money extraction with YouTube but that's not my point, my point is that YouTube now has a monopoly and any actions that threaten that, such as strongarming people into watching 3 preroll unskippable ads, are in my opinion silly and self-defeating.
They're just too greedy. If they made the price of YouTube Premium something reasonable ($1 or $2 a month instead of $14 or whatever it is) they would get a lot more subscribers and probably even get more revenue. $1 or $2 is not worth spending even 10 minutes digging in obfuscated JavaScript to fix an adblocker, so this whole thing would go a lot smoother for them if they charged that. Even if $14 is not a lot people just don't want to pay that much.