[bunderbunder]

It might be the particular OOP languages you're used to. Ruby, PHP and Python all have pretty strong cultures of relying on mutation and side effects. Part of this might be that the languages are so focused on dynamicism that you really have to go out of your way to even suggest that a type should be immutable. And even then it's only a matter of time until someone mucks it up by applying a mutable mixin to the type.

In other languages, though, it's perfectly possible to create immutable classes that can only be interacted with using pure functions. You could argue that it's questionable that these do anything you can't do better with records and algebraic data types, and there's something to that. But there's also something to taking the pragmatic approach and not letting the (presumably) remote odds of your employer adopting a niche language prevent you from writing better code.