Why should I want to do that? Jaibroken devices should still have access to the app store.
They do but apps get signed to the latest firmware and sometimes this firmware can't be reached on jailbroken devices although this isn't problem at the moment it may well be in the future.
The second reason is pretty weak to be honest but it's that updating all the jailbreak apps and reconfiguring them can take awhile it's not quite as easy as proper app.