A lot of people have Chrome installed alongside Firefox or Edge or whatever and will just try the video somewhere else. So YouTube actually gets more revenue and Chrome gets free advertising. If a major website works on Chrome but doesn’t work correctly on Firefox most users will tend to blame the browser instead of the website and think “I stopped using Chrome because of the memory issues but at least it’s reliable.” The logic even sounds superficially reasonable.
It's a trade-off. Which way do they gain more money? From showing the YouTube ads to Firefox users, or from getting users into the Chrome ecosystem for however that is monetized?
I don't see how breaking YouTube for a portion of the world population is a sensible part of that plan.