What use case are you referring to? I don't know anyone who uses ratings sites after seeing a movie.

My point exactly. And why would you care about rewatchability if you didn't see the movie once?

rewatchability should indicate a light-weight movie. If you want that, you look at rewatchability, if you want something more complex, you use quality. I think this is the underlying assumption.

I don't think this is right. People watch movies like Blade Runner and Citizen Kane repeatedly.

Possibly to know whether you should rent it or buy it.

Because the rewatchability rating doesn't just tell you how rewatchable a movie is, but also how good and "timeless" it is, i.e mainly how deeply it resonates with people.

This is not about picking a movie to watch again after you have already seen it once: this is about picking a movie you haven't seen but that is so good that other people like to watch it again and again.