it is hard to read if you don't have some knowledge of haskell indeed and the comments part is true but it's not any harder then folowing other codebases if you don't know the particular language so i don't think this is a strong argument.

Another point is - it's not a library and you are not the one maintaining it :) the same way you are not maintaining, but still using things like postgresql,nginx,redis, rabbitmq.

I bet it's a lot easier to learn haskell and patch postgrest then to know C for 10 years and patch postgresql :)