> I understand why this doesn't work well with legacy projects, but it's something that the language could strive towards.

Why wouldn't that work well with legacy projects? In fact, the projects I was a part of that I'd call legacy nowadays, was in fact built by copy-and-pasting .js libraries into a "vendor/" directory, and that's how we shipped it as well, this was in the days before Bower (which was the npm of frontend development back in the day), vendoring JS libs was standard practice, before package managers became used in frontend development too.

Not sure why it wouldn't work, JavaScript is a very moldable language, you can make most things work one way or another :)(