The problem with jailbreaking is that it is unsupported by the device manufacturer, and AFAIK Apple is even actively trying to prevent people from doing it by closing the security holes that are used to implement the jailbreak. (The same limitations apply to WP devices also...)

Hence, when you have a jailbroken device you cannot really be sure of the integrity of it any longer, and you are also lacking the OS upgrade path and need to do it all over from the beginning if you want to get an up-to-date OS.
I have been told that many of the functionalities of the jailbroken devices are not implemented very well and work more or less haphazardly due to the obfuscated nature of the device, as developers and hackers work pretty much in the dark due to the closed nature of the device.

It just seems so silly to fight an uphill battle, when instead you actually can get a device that is developer-friendly and that lets you can gain root access by using manufacturer-approved process.
A device where you can install both official OS upgrades and your own tweaks/modifications/applications by same package manager (and where you can indeed create your own packages on the device itself if you so desire)