Ok here's a talk about making Haskell games that took place last week: https://keera.co.uk/blog/2019/09/16/maintainable-mobile-hask...
I don't deny that making games in Haskell is niche, but it's certainly possible. Frag was just an example I remembered (ten years is recent for an old git like me).
If I remember correctly, in that thesis the author mentioned explicitly that the game didn't run very fast. If you watch the video from 2008, the in-game stats list framerates >60fps but the game itself is very laggy. Maybe there is a separate renderer thread?
This particular solution used functional reactive programming, essentially a composition of signal/event processing functions/automatons.