[montanonic]

Honestly, I think for a lot of people who've used both Haskell and Elm, the answer is pretty clear: lots of Haskell in the wild can be very hard to read and think about, even with significant time invested in it; and when it simple to read, it's likely not using many more features than Elm is. Yet, even with a very strict subset of its features, it is a very expressive language: sum and product types are an incredibly powerful concept; I'm blown away by how much more straightforward managing state is with them. Expressive types and superb type inference generally make refactoring a breeze. There are just many huge wins overall.

But you can have the bulk of these wins in a simpler language like Elm, or a language like Rust which tries to only add more type complexity in cases where it would significantly improve code in practice, rather than in theory.

Haskell is necessary; it pushes the state of the art forward because of how experimental it is (compiler extensions). But it's pretty clear that the community is skewed towards research rather than industry, and culture strongly influences what a language is practically capable of.

This does not at all mean that Haskell isn't fully capable of industrial applications; we have direct evidence suggesting otherwise. But with a philosophy to "avoid success at all costs", it should be fairly clear that moving out of the realm of obscurity isn't exactly a goal of the language.