I imagine it also might have something to do with the difficulty of upgrading a jailbroken phone. I try not to upgrade more than necessary because I don't want

I imagine it also might have something to do with the difficulty of upgrading a jailbroken phone. I try not to upgrade more than necessary because I don't want to go through the hassle of having all my settings potentially erased after upgrading, only to have to put everything back the way I want it afterwards. There's also the issue that jailbreaks aren't always available right away for the latest version. They usually take a few weeks to appear after releases.