For what it’s worth, while I’m perfectly comfortable with HTML and CSS, I prefer JSX + CSS-in-JS. This isn’t because it’s one language versus three. It’s because it promotes colocation of related code, and allows a high degree of composability that’s much harder to achieve otherwise. Colocation is great for understanding what a given thing does, and for identifying its dependencies. Composability is great for mapping a domain model to lower level concepts in a coherent way, and for encapsulating dependencies.

This is somewhat achievable with separate languages. But it ultimately takes a very similar shape with additional tooling/ceremony and diminished benefits particularly from colocation.

Nonsense, we do it all the time, we just do it under the guise of Javascript. We just turned HTML into JSX and put our CSS in template literals.

Exactly.

Not that amazing. People who build languages are people who like languages, and therefore have tried a lot of them and find learning new ones easy and rewarding.