Other languages also have advantages in certain areas, e.g. Node.JS lets you reuse the same code on the server-side and client-side, something which is great for those wanting to right games that require the server to simulate them and the client to run them.
Even if the language is rarer, say C or C++, there are still many circumstances where it is better to use those than it is to use Python.
I do not foresee any language to be able to be easily usable in every use case, the generality itself would be a drawback for specific user case. There is a reason there are currently dozens of popular programming languages out there.
Also it's great for SSR.
Don't have to worry about if the join function has different signature per language.