I think it's important to remember that the Snowden leaks occurred shortly before the "Big Data" craze went into full swing. Even Snowden said at the time that

I think it's important to remember that the Snowden leaks occurred shortly before the "Big Data" craze went into full swing. Even Snowden said at the time that their was more data than could be effectively analyzed. While I agree with what you're saying, it makes sense that we'd be getting this information only just now - after there has been enough time for 1) data scientists and the like to become prevalent/cheap enough for government contracting and 2) enough time to build working applications on top of all that data.