I don't know why Microsoft or Amazon don't try to launch a YouTube competitor. Vimeo probably has the most reach for an acquisition, but those are more artsy/professional focused. I suppose Facebook is YouTube's largest competitor, but it's such a closed system that it's impossible to use in any manner that isn't strictly personal.
I know it wasn't profitable 3-4 years ago, but I believe it's fairly profitable now. But I'm not sure, I suppose the cost of running a video service can shift so drastically it's hard for it to be steady. I don't think Alphabet breaks out YouTube revenues/profit anymore.
Last year the initial event of the "adpocalypse" happened, which both demonetized a lot of channels, and at the same time roughly halved what advertisers were willing to pay, even for complying channels. Since then a few additional waves of demonetization happened.
Every time Youtube demonetizes a creator they are also demonetizing themselves. The combined effect of all that could have held back profitability significantly, especially considering that they are shooting for comparatively low-margin advertising business model compared to other platforms.
And thats why we see a lot fewer new social networks starting out today. in the late aughts, everyone and their grandma was starting a social network, google started 3, heck even apple started one, everyone was trying to replicate the perceived success of facebook, when even that wasn't yet clear as a viable business. Now that most people know just getting lots of eyeballs doesn't translate to cash in the bank people have cooled off.
youtube is an even bigger issue because video is so expensive to support, so on top of the possibility of not making any money, you also need to front huge costs in infrastructure.
And Microsoft has Mixer, but they aren't YouTube competitors. Maybe for LiveStreams, but nothing else. Amazon is more strict than Microsoft on what can stream and what can't.