Why do people dislike JSX? For me the lack of JSX is a negative point. Why would I want to write nested functions everywhere? JSX is HTML on steroids, but it can be just HTML if you wish it.
Is this the main argument? I think the simplest answer is boundaries. Taking into account how much nesting is involved in writing HTML, it's a clear benefit having a named boundary vs a closing parenthesis.
Too much nesting usually signals that you should decompose it to smaller components.
Same as with regular code and functions — overly deep nesting screams bad code.
Honestly, JSX is just a verbose way of calling functions / constructing objects, which is probably OK if it was a language of its own (XML/HTML) — and even then, JSON/YAML won over XML — but makes little sense being embedded in a language which had functions & object literals from the get-go (JS)!
The only reason JSX exists is because it was a cool marketing feature to convert existing PHP/HTML developers to React. And React succeeded mostly because of that. Not because JSX is cool technology-wise (it isn't). But because it hit the right spot in the right time.