The problem Cabal is trying to solve here is supposedly more difficult than that solved by Gem, Pip, and other package managers. GHC does some kind of cross-library optimization that causes dependency problems in routine situations.

I agree we shouldn't have one package manager per language, but I think so far no one package manager has proved sufficiently general and robust to serve all use cases. For example, I think something like Nix would be wonderful for all language communities, but it doesn't run on windows. That immediately takes it out of the running. And as far as I'm aware, all other package mangers would have the same "Hell" problems of cabal because of the GHC optimization mentioned above.