I had a discussion with one of my friends the other day that might shed some light on this issue. We were talking about the kind of movies we like. He likes what I call "true sports" movies--that is, movies about sports that are based on true stories, such as
Cinderella Man,
Radio,
Remember the Titans,
Rudy, etc. He was deaf to my criticism that such movies are almost always based on formulas to provoke the "right" responses from the audience, and they make use of storytelling devices that create a new "reality" instead of accurately reflecting the vacuum of meaning that characterizes reality until some human comes along and imposes a personalized template upon it to give it meaning. For example, the "villain" in
Cinderella Man wasn't really a villain in real life, but the moviemakers turned him into one to improve upon the original story. The result is not what I would call "realistic". But it's a "true sports" movie, so my friend likes it. He doesn't like movies such as
The Lord of the Rings or
Spider-Man because they're not realistic.
There lies the difference between us. I like movies that
aren't realistic. I want to see fantasy and fabrication. I want to see a new "reality" that has been shaped by a human mind and therefore given structure, meaning, and significance. I'm fond of humor and irony, which are totally invented, as well as symbolism, adventure, and struggles between good and evil. That makes me a good viewer for a movie like
Spider-Man. It also makes me a good candidate for roleplaying games. I'm not saying that there are "two kinds of people in the world", but the friend I mentioned is a different kind of person than I am, so he's not the type of person who would enjoy roleplaying games.
I don't know if I could tell you what kind of people like to play Baldur's Gate. But hopefully I've given you some idea of why I enjoy playing it. It's a structured fantasy environment that has meaning to me, it deviates from real life in ways that are fun and compelling to me, and I enjoy being immersed in a world that isn't real.
My experiences with pen-and-paper D&D are mixed. On the one hand, I enjoyed the immersion, and some of the adventures I had with my friends were fun. I enjoyed playing with other people because the group dynamics gave the game the kind of spontaneity and unpredictability that can't be reproduced in a "canned" game. No DM could anticipate our reactions, so any DM who tried to railroad us was in for a real treat.

On the other hand, the gameplay itself was very frustrating. Baldur's Gate runs very smoothly in comparison. I also enjoy playing alone because I can go at my own pace and make my own decisions and use my own imagination without having to negotiate with anyone else.