I don't thinks it's quite that simple, there are other factors as well:

There are significant network effects. Content creators use youtube because there are a lot of viewers watching content there, and viewers use it because there is lots of content there. Since YouTube already dominates the market, it is extremely difficult for another platform to compete, even if it was better in every way.

Google can promote YouTube using its other monopolies/oligopolies. Most notably, google search prioritizes videos on YouTube over other videos. Also, being able to pay for video ads and search ads with a single vendor is probably actractive for ad space buyers.

Google also already has its own CDN, which probably reduces the cost of distributing the content.

I think this network effect and the discoverability aspect are the main reasons why it's extremely hard to compete with YouTube. Why would people use another site if the content they want to see is not there, or is too difficult to find? Why would creators put videos there if they can't find a large audience?

The YouTube algorithm is problematic in many ways but it does succeed in viewers being suggested videos they want to see, even if the signal-to-noise ratio is not very good. That's hard to replicate when starting a new service.