When I talk to people who play games about writing, and why they should write, the most common complaint seems to be this:
There's no random element.
When you play D&D, you have a table full of people. Hopefully, they'll behave in interesting and unpredictable ways: they do unexpected things when it's their turn to choose actions. They say funny things at the table.
This is why most people get out and do it, after all. The fun is in not knowing what comes next, and having a story to tell people afterward. Or, well, it would be if anybody wanted to hear stories about D&D. :)
Even if you've never played D&D, most social activities work the same way: you get together with friends, and hopefully something interesting happens. Something you could talk about later.
A lot of people who haven't written think that writing lacks that element of chaos and fun. They don't seem to believe me when I tell them that it's still there, that writing a story is random and strange and surprising. They don't understand that I write so fast mostly because I'm eager to see what happens next.
Rather than just repeat myself about this, here's an analogy to consider:
I'm going to go out on a limb and guess that everyone reading this, (all four of you), have played Solitaire. It comes free on Windows. It's right there. If you missed it somehow, you should really try it*. People like Solitaire. On road trips, I've seen a version that you play holding the deck in one hand so that you don't even need a table.
What's interesting about this game is that every element in it is fixed, once play begins: it's just you and a set arrangement of cards. There's nobody to outwit. You don't shuffle the cards again, once they're dealt.
The outcome should be predetermined. There ought to be no reason to play it in the first place.
Except, as we all know, there's a little more to it than that. You can be surprised by the game. You can still lose, even though there's nobody to lose to.
The reason it can be fun is that even though the cards are dealt, you still have to make choices without seeing all of them at once. You can't track the whole deck and say with absolute certainty whether or not taking out any given card is going to help you or hurt you in the long run.
Writing's like that. You have to make choices about dialogue, actions and plot without understanding all of their potential implications. You can paint yourself into a corner or strike genius accidentally. Small choices sprawl and grow.
This allows something that looks static from the outside to be full of delightful surprises when you really get going. I think most people would enjoy what that feels like, if they just gave it a try. About the only thing I can compare it to is falling in love.
* (Disclaimer: I'm more of a Freecell man, myself.)