I think the lack of higher order functions is a huge part. If you don't have built in higher order functions, you have to add 1 interface per function taking a higher order function and 1 class per different call. From there on, you have to manage all those extra classes and interfaces somehow, which easily spawns more classes you wouldn't need otherwise.

These resulting structures then end up being factories (You could pass the object creation function), command objects (you could have a function to call instead of a command to pass back) and so on.