Wait. Is this true? If so, that's cool. I know your comment was sarcastic, but as a grad student in math I've futzed with category theory enough that those words mean more to me than the raw Kleisli triple definition.

It seems you're talking about the IO monad specifically, not about monads in general. Other monads, like Maybe and List, absolutely occur in programs written by "most developers in other languages", whether they perceive them as monads or not.

For instance, a pointer type in C is like a "Maybe a" in Haskell, because a pointer can always be null (Nothing).