It's the old rule known to governments all over the world - there is no such thing as an innocent citizen, there is only a citizen who you haven't investigated enough. Call me cynical but storing ALL of your digital data allows the agencies to basically find something, anything, that will allow them to further blackmail you into complying. Even the most innocent person will have something that can be misconstrued as criminal, from jokes about tax evasion to pictures of your toddler in a pool - threaten going to trial if the person doesn't do X, and most people will comply, not because they aren't innocent, but because the might of the American justice system is such that you really don't want to fuck with it on the receiving end.