3 things:
1) Clearly, you haven't played a lot of PnP RPGs: I've been in several games of D&D where I got railroaded massively, and it ruins the playing experience for me there as much as it does in a computer game. No: you can't kill that character, he needs to be alive in the next adventure I run, so he gets away, even though you do have a crossbow pointed at his head, and a readied action. Actually happened to me.
2) MMORPGs are worse than single-player ones, for the most part. It's hard to feel special about being a lvl 40 character (which is supposed to be higher than "normal" people are) when everyone around me is lvl 80. And since there's so little difference between the character builds, I begin to wonder why someone hasn't solved this problem before.
Oh wait. Everyone already has, but I need to do it again. Because I do.
3) If you really want one of these: try it yourself. Trust me, it's hard. It takes me 10-15 hours to prep for a once-through game of D&D at a convention: 8 hours of play time; and I'll be surprised once or twice, usually because of a PC ability. I've spent maybe 800 hours building a world, and still had to make stuff up on the spot repeatedly (at least one session had over 10 surprises) for the maybe 400 hours I've DMed said world for a weekly game. That group, just playing as they did, required me to flesh out some NPCs I had barely described, build NPCs that never existed before, build places that never existed before, and much, much more.
If I wanted to take an estimate, I'd need about a year of work, 2-3 hours a day, to build a small city (5 000 or so people) complete enough to make sure I could never be surprised in it, and flow with any action a person could take. However, remember that the "computer" running that city (me) has a built-in improvisation, emotion, and creative drivers that no digital computer can come close to emulating.