Meh, I think IDE integration is an essential feature of a language. That’s why I use VS Code any time I write JS and only then.

Now imagine the only option to write JavaScript in a sensible way (however this should be possible :-) would be VSC. Do you really think JS would have had any success? I think it would have been another Visual Basic.

Even typescript (a MS product) can be written with all sorts of IDEs/editors.

If we could only use VSC, that would be fine because VSC is fantastic.

I've found the same of IntelliJ products. They're so good that I don't mind being forced to use them.

C# and Swift are in that boat (VS and Xcode) but they’re doing alright, because they’re the main blessed languages for their platforms. JS is the only blessed language of web front ends. So yeah I don’t think IDE lock-in is a concern for JS but it definitely makes me happier as a developer to have deep integration that makes my job easier.

If VSC + JS would be free, open source and running on all platforms, why not?

Sure, but it's like windows and .net, even if they invest in usage outside their own native ecosystem it's going to be lackluster.