> As a result, it seems that most Haskell programmers don't even try to understand the control flow of their programs, because it's almost impossible.

The abstractions used in Haskell code almost always use existing and already well understood abstractions such as Monads, Monoids, Functors, and Applicatives. I most certainly have to understand my control flow in Haskell programs and it is not impossible.

> There's certainly no shortage of abstraction in Haskell code.

I've typically found said abstractions to be sound and needed (or at least justified) however.