Probably for the same reason a lot of us have played it more than once, myself included, as I've gone through dead money more than 10 times now.
We enjoy the DLC.
Well, that's cool. I just finished up Dead Money. As you can see from my post I had a few problems – probably because I am playing on the PS3 – but I'm sure there are bugs and glitches on other platforms. These are very complicated games and I try not to let the technical imperfections get in the way of my enjoyment of the game. However, I just didn't find Dead Money to be that compelling of a release - especially when compared to the grandness of the Fallout 3 releases. While I certainly enjoyed the minor added mythology of the side story elements from the main game, I really found the gameplay to be tedious and repetitive. The environment of the Villa was rather dull and while I did enjoy sort of being forced to sneak around more than usual, the gameplay device of: find the 3 people, take them to the fountain, take the three people to their spots, then go to yours, go into the casino, then find the three people to be quite redundant. It really seemed like a waste of time for what could have been a better gameplay scenario given the circumstances of this small story. Not to go on a rant or anything here, but there were small aspects of it I liked, but for the whole I thought it was rather weak, rushed, and seemed to have little involvement from anyone involved in the production of New Vegas-proper. Basically, I just couldn't see myself playing through it again, much less two more times – such agony. I'm happy you enjoyed it though.
It's just after playing through the regular game for about 80 hours, doing all of the quests I could find, then playing Dead Money – I was admittedly let down. I'll probably start up Honest Hearts in the next few days. I believe I've heard its rather short. I am, however, really looking forward to Old World Blues.