I can only speak from my own experience, but expressing a program as a composition of pure functions, where effects are carefully managed, is a challenging way of thinking at first. The imperative approach really is simpler to wrap one's head around _until you start worrying about correctness_. I think many developers never really care that deeply, so Haskell never appeals to them. You really do have to take a mathematical approach to program construction. I personally think that the mathematical perspective is liberating, but it's not an easy one to cultivate.