A good reason(s) as to why there won't ever, ever ever be sequel.

1. Geo-Stigma much
2. Whacked out
3. Levi would kill a serious amount of people
4. Levi would probably be the villain
5. So would Kumo
6. The world would explode

I'm sorry. I'm bored. I drank 500ml of V.

EDIT: 4&5 make more sense if you play the game to its fullest extent and fight all secret bosses.