It's one thing getting spied on by the US government, but one would hope they'd use something more sophisticated than Hotmail to move the information around.
It's a dead drop. If this was cold war era Moscow, they'd use a drainage ditch or a loose brick. Hotmail is just the digital equivalent.
Trouble with that is, the more sophisticated and unusual the mechanism you use, the more likely it is that someone will (a) notice you, and (b) be able to identify you based on it.
That's my theory. Any monitoring of outgoing information would just see a typical attachment to a hotmail address.
Hotmail seems like a reasonable first link in the chain to extract the information. I assume they would log in through Tor or another anonymous method before extracting it to its final location. They're not going to email it to joe.spy@nsa.gov directly.
Well, it was encrypted, and they can't exactly send it to "nsa.gov", can they?