Like a poster said earlier, it's becoming harder and harder to find exploits in the iOS. Plus, the top JB'ers have lives outside of hacking. To them, a JB isn't everything. And they spend countless hours trying to JB an iOS version only for Apple to thwart them and release the next one. I have a bad feeling that iOS 6.x will be the last version that will be JB'ed as iOS 7.x will probably be unjailbreakable.