Nah, I think its just because they result in really nested types which is hard to keep track of without a really good type system. Using a single monad by itself like error or continuation is straightforward in Clojure; there are smart & vocal people who do this. But the super awesome OMFG of monads is that they can be combined (e.g. parser = error + state), and this more or less requires abstracting in the type system to keep track of all the lambdas.