Just because it happens, doesn't mean it makes sense.
Anyway, people write their own game engines, and programming languages for game engines, because it is intellectually stimulating to do so, and something you spend 100h/wk to yield 1h of gameplay is still giving you more gameplay than something boring you spend 0h/wk on.
Then, the people who use those engines you are naming, they end up porting to Unity anyway. If you want to deploy on iOS and Switch with one codebase, it is the only game in town. And that's sometimes 60% of revenue.
> Don't underestimate what an individual or small teams can produce if they are operating on a solid platform that facilitates a rich ecosystem of tools.
Unity fits this bill exactly. I too want more competition. But in the real world I live in, if someone were to ask me, "what solid platform should I choose to make my multimedia application, as a small team, that also has a rich ecosystem of tools, and will enable me to make pretty much anything I can think of?" I would say, use Unity. Because I want them to succeed.