Maybe they just don't care that the US government read their emails, its mostly spam or junk anyway.
This. The majority of my emails are just stuff like Youtube subscription notifications, or, me asking someone where they're going to be on XYZ and if they want to do ABC. Unless the NSA cares where I'll be on Feb 11th (Believe me, it's no where interesting, not planting any bombs or anything), then, they're shit out of luck.