Simple answer is I don't. But I'll answer.
I concur that it's adventure-y. I've grown up experiencing the same characters (in quests) and want to stay with what happens. Same principle to why we play games like GTA?
It's simple, easily accessible. Not to difficult to figure things out in the game and still enjoy some complexity.
Another huge reason is it's good to socialize on. RS has lots of activities you can do with other people and talk. It can be relaxing.
You get to choose what you want to do with your character. Lots of freedom and part of enjoying a game is being able to do what you want, enjoy any aspect of it and not get too bored of one thing. A big part of this is there's always something new, so unlike a game like Call of Duty, there'll always be fresh content.
