I don't personally find that appealing at all, so I'd be surprised if I hear that is the answer some people have. But I would be pretty curious to hear if that is the case for some.
I enjoy all of the RPGs to some extent and really loved the first few, but barely anything about an actual RPG would translate well to what this game is trying to encourage.
It's funny, thinking about the term now, this is less Pokemon the Role-Playing Game and more Pokemon the Actual-Doing Game. I mean obviously you aren't legitimately catching monsters and battling Gym leaders. But it's (unless you're sitting in one place clicking pokestops every 5 minutes for hours at a time) a very active and atypically social experience using some of the really comfortable and addictive concepts from the original Pokemon idea: catching your own creatures (you can name them), evolving them, getting jelly and wanting rare ones really bad, battling them against other ones. Those concepts are all here and just as strong as they were in 1996, but the "mechanics" aren't even remotely RPG-like.
Pokemon Go is a 0/10 RPG. Like, -50/10. It actually feels a little more like other activities than most games in general, I guess sort of more like a board game or LARPing minus the RP plus technology? Or I guess to be perfectly honest, it doesn't really feel much like anything else that exists so far as I know, except for Ingress. Which has no pokemon at all.