Well, if they are intercepting data through backbones, and much of that data is encrypted, they need to defeat the encryption in a durable way to get a clear feed. While I don't suggest that this is what was going on, if it was, there would be know reason that each provider would necessarily be broken at the same time; there would likely both be prioritization of resources directed at each provider, differences in the security of each provider, and chance involved as to when each was broken.

Growing popularity and usage of icloud and apple's own messaging system? iirc, before icloud, Apple didn't have that much user data.