That's actually an interesting question in itself. Google also has a domineering (though not monopoly) position in ads. If someone were to try to compete with an ad-funded service… how much of a problem would that be?

Also: part of the problem is the quality of the ads. Could you actually get "better quality" ads for a competitor video platform? Do such ads even exist in sufficient number at this point? (I vaguely remember a significant portion of larger companies reducing their internet ad budgets because they simply weren't seeing good returns…)

There is a very interesting example, but unknown to western readers. It's called Bilibili.

It's the largest video platform in China[0]. However, it keeps losing money since forever, including in last year, and is expected to keep losing more in 2023.

[0]: Youtube is blocked in China and you need a VPN to access it there.