The thinking that key exchange need to be robust and P2P makes alternative secure solutions harder: most of the times big companies don't want to be caught doin a man-in-the middle attack, so iMessage or even Facebook is practical enough for it, as long as the key exchange can be verified on any other comunications channel easily.

We would be in a much better position right now with email privacy if the version of PGP that doesn't defend from an active attack would have been deployed worldwide.