Snowden was low-level, but he was basically an admin doing migration to a new system. His job description required the access he was given.

Additionally, one of the lessons learned from the 9/11 attacks was that keeping data too "Need to Know" might prevent people who actually need to know information from knowing about it.

I'd recommend you read Greenwald's book, "No Place to Hide". Snowden was not exactly "low-level", he was in training for operations. He backed down to a low-level position by choice when he wanted greater access to documents. He even took a pay cut to do so.

This has been made worse by the fact that they classify almost everything as secret now - while at the same time they still have to show many others those documents. When doing that even labeling stuff as "top secret" tends to be done a lot more often (when it's not necessary), which only dilutes the secrecy of the real top secret stuff, mixing that together with the less top secret stuff, and making it just as easy to be leaked and/or shared.

When you have 10,000 documents labeled "top secret", instead of just 100, who really knows what's really important from that list, and doesn't need to be "as shared" anymore?