That's because real-world Haskell tends to not be idiomatic, and it involves a lot of directly telling GHC what to do. Mathematicians don't have to (and rarely, if ever) make efficient code. GHC is a really advanced and impressive compiler, but that really doesn't amount to much. At some point the language just devolves into understanding what arcane compiler internals you need to invoke, and it's more like a bunch of C macros with a fancy runtime.
