The learning curve to PureScript is way higher than Elm. Is that not that obvious?
I think there is a good free introductory book [1], a welcoming community [2], the language and ecosystem are quite stable nowadays and there's good tooling (now that there's the Spago package manager).
[1] https://leanpub.com/purescript/read [2] https://discourse.purescript.org/
The 'Pure' is the problem here.
Also, these days no one want to learn Haskell just for sake of building UI. Just do it in JavaScript or TypeScript, far far far easier pill to swallow.
Yes I learned Haskell, Elm, and Rust