Let’s say I was the FBI, and I found a fantastic back door into the iPhone.
What would I do with that information?
Well, I might very well pick a very public fight with Apple, demanding that they open their phones’ firmware. And ensure that the disagreement with Apple was well-covered in the media.
“Apple won’t open their phones for the FBI.” Terrorists would muse. “We can use iPhones, and the FBI won’t be able to get to our information.”
Like I said, just a thought experiment.