Am I being too cynical here?
My guess is that the FBI decided that there was probably nothing of interest on the phone (after all, the user destroyed their other phones but not this one), but they didn't want to risk proving this. If Apple gave them what they were asking for, the decrypted data would then show incontrovertibly that this was the case. If a third party makes a less definitive attempt at it (e.g.a bungled one), the FBI's PR can spin it to their advantage.
Biting the hand that feeds IT
