VSCode runs nicely on my MacBook. It doesn't feel like a web application to me, in the same way that IntelliJ IDEA doesn't feel like it's written in Java. I'm sure that both VSCode and IDEA could run even faster if they were ported to, say, C, but in both cases that would be a large investment for improvements that I wouldn't even detect.

So I guess it makes sense to optimize for maintainability i this case, i.e. not having one codebase per native OS.