Not every phone has a jailbreak available for it. Plus, you're still stuck with an effectively sandboxed kernel. You can't fix any bugs or implement any kernel

Not every phone has a jailbreak available for it. Plus, you're still stuck with an effectively sandboxed kernel. You can't fix any bugs or implement any kernel level drivers, for example. If I need a new IOKit driver class, I simply build the kext and use `kextload`, or I can just prelink it into the kernelcache.