Btw, the reason Haskell isn’t used more isn’t type system per se, as all types can be inferred at the compilation time. People would sometimes use this feature even to see if GHCi guesses the type correctly (by correctly I mean exactly how the user wants, technically it’s correct always) first time and save them some time writing it either with an extension or just copy&paste from the interpreter window.

When it gets hairy is that most programming languages have low entrance barrier. To write Haskell effectively you’ve got to unlearn a lot of rooted bad habits and you get to dive into the “mathematical” aspect of the language. Not only you got monads, but there’s plethora of other types you need to get comfortably onboard with and the whole branch of mathematics talking about types (you don’t need to even know that such a field as category theory exists to use it).

However, since most people just want to write X, or just want hire a dev team at price they can afford, Haskell rarely is the first choice language.