On the topic of other languages taking over these tools, fundamentally it comes down to this: At the end of the day, these javascript tools (beyond just npm/yarn, which I think could be written in any language much more easily), like webpack, babel, or rollup etc., create very hard to replicate advanced ASTs. Even microsoft hasn't bothered to port typescript compilation to say, C# or F#, and I think largely because its a lot more complex to create the foundations for those languages to understand javascript on that kind of level.

You could argue (and I can see the validity of it, see the Closure Compiler for a counter example), that it can just as well be done, but it seems like its far easier to implement in JavaScript these kind of tools.