It's a big ask to want integrated debugging, project management, advanced semantic search (go to implementation in child class), and semantic manipulation (extract these methods into a new class) for all the languages you happen to want. Perhaps it's possible, but it's a huge project.

It's at least an order of magnitude easier to support viewing, editing, syntax highlighting, and textual search across arbitrarily many languages, which is why there are many tools that support that feature set, including almost all major code editors.

I don't know how JetBrains architects their IDEs, but I suspect they have some in-memory database that populated with indexed project metadata. To add multiple metadata indices (for different languages) with cross indexing between them would be an entirely different data model. Again, it would be much more work to develop, test, and maintain.

In IntelliJ IDEA Ultimate, you can install all language plugins for no additional cost. However, project initialisation and management gets a lot harder with several language plugins enabled. The language-specific IDE from JetBrains will still be easier to use, but for a price.