Haskell's laziness and purity can make it a bit trickier to use constructs that are common in ML-like (or Scheme-like) languages, like mutable variables. This nudges Haskell libraries in a slightly different direction, e.g. making more use of control structures like monads, arrows, continuations, etc. which authors in other languages wouldn't reach for so readily. This has an effect on the ecosystem, since people want their systems and libraries to be compatible with each other's APIs.

The result is that "the Haskell way" can seem a little more intimidating than the more "pragmatic" approach of MLs.

(I write this as someone who writes a lot of Haskell, and dabbles in StandardML!)