Sure, but Kotlin is more about being explicit and less about evangelizing one style of programming over another. It's very pragmatic in that way. There are plenty of scenarios where you're maintaining local state (properly encapsulated within a class, exposing a functional interface, etc) and you need mutable fields. Even plenty of scenarios where you want to operate on a value mutably in a function and then return it. It may seem confusing at first but in practice I've never mixed the two up.

But this most likely is because Scala uses val/var.