Why We Likely Won't Get A Sequel For "Zombieland"

Collider brings us the following from Ruben Fleischer about the chances of a sequel:

Well I think that the studio would be very excited to make it.  It's not that the studio is not excited, it's that we took one shot at the script [and] it wasn't something we all got excited to do.  And just on a personal level, I was really excited to, having made one movie, to make different movies, not just go back into that world again.  But now that I have some distance and I've done some other stuff, I would be more inclined to go back to Zombieland I guess you could say.  But at the time when the talk of the sequel was really--when it felt like it was possible--I was really kind of shying away from it just because I've only made one movie, I wanna make different movies with different people and learn different things, and so I was a little hesitant to just jump right back into the same thing... 

Needless to say it was a continuation of the original story with the same characters.  I guess the only thing I could really say is that the threat to our heroes wasn't only zombies, like they encounter other people that they're all jockeying for positions.