Also it was very tempting to have JSX compile into literal strings, effectively being a composable variant of tagged template literals with better IDE support,

Also it was very tempting to have JSX compile into literal strings, effectively being a composable variant of tagged template literals with better IDE support, so that <a href={123}/> compiles to a function that returns `<a href="123"></a>`. It would have simplified the conceptual model significantly, and the implementation almost as much. But because it would still be joining a bunch of strings together, it's literally about the same speed as the current implementation (which just adds the whole tree to a single array and joins it only once), so there's no real gain there. And we lose script/style/tag hoisting, which is necessary for components to work the way they do, unless the JSX system is hacked in another (less simple) way to allow for it than currently.