Youtube does not have a monopoly because it's the only video app installed on your computer, but because it's the one everyone uses.
Plenty of people have tried to compete, but Youtube was good enough. Others had good reasons to try but concluded that Youtube was good enough.
When Youtube is no longer good enough, they get to show they can do it better.
Google search is worse, because it hasn't been good enough for a long time, but somehow every competitor has decided to be worse. Altavista 25 years ago beat what Google search is today, I can't imagine Microsoft being unable to afford to bring Bing up to Altavista levels.