Well non-web GUIs have been basically stagnant for a good chunk of that 40 years :)

You're right that it's OO under the hood. The latest thing I've used is CLJFX which is a React-like wrapper around JavaFX. I don't feel the OO side has much effect on my experience using the library. It's still events, callbacks, state-updates. The class hierarchies are irrelevant to the library user the vast majority of the time.

I wouldn't be surprised if for the library writers it provides benefits with code reuse and type gymnastics. But for mere mortals that need to refactor and reorganize our messy ideas OO hierarchies seem scary after React-like development.