This doesn't just apply to MVC but also for example the Elm architecture. The thing is that they are quite simple in theory but in practice, programming them from scratch can be much more difficult, mostly due to the View.

For example, what if you have two widgets that need to be side by side? And the user needs the ability to use the keyboard to switch between them? What if now you have a third widget below them that is also tabbed?

At this point you need a state machine to track the state and where the user is currently at. It's easy if this is done for you but pretty difficult otherwise in either architecture.