Why? Silicon Valley VCs know exactly what they are building - massive repositories of user information to datamine for the highest bidders.
The NSA does not require exclusive use, is independently funding datamining research, and has subpoenas - so they are a natural early client.
These facts have been plain as day to anybody who thinks about the implications of their technology choices. Most don't, so the services become widely adopted and even quite hip (unfortunately).
Snowden comes along and ignites the media in a way that Binney and Klein hadn't, just as the pendulum is starting to naturally swing towards decentralization. It is now in the public consciousness that perhaps these companies are not to be blindly trusted with the contents of your life.
Of course Andreessen is pissed. The entire business model of modern SV has been illustrated.