Why doesn't Apple prevent iPhone jailbreaking by encrypting iOS and installing it on an independent chip?

With this I mean iOS will be encrypted with AES or any other very strong encryption algorith to prevent jailbreaking. It would also have its own storage chip, where the OS is installed. Any attempt to access this OS chip would result in the OS being deleted and the iPhone being useless if attempted. Only certified apple technicians could then fix your iPhone.

So why doesn't Apple do it to prevent jailbreaking?