I'd say PGP got us to the point where endpoint security matters, and Apple closed the loop. Allegedly that's why they want the phone so badly: to dump data from encrypted messaging apps.

The FBI long ago adapted to breaking open general purpose computers that were encrypted by i.e. keeping them awake and logged in through arrest and seizure. PGP won't do you any good there.

Apple finally built the walls around the garden high enough (by doing security at the hardware level) that they put up a fight even when the device is on and ready to use.