I kind of wish he would too, but this is actually probably necessary to end up having the discussion this deserves.
If he had released it all in one big dump, it would have spent a week or two in the press and be a distant memory.
As it is, Greenwald (I suspect more than Snowden it's Greenwald managing the publication - it's his field of expertise after all) releases data, NSA flaks come up with stories and denials and lies, he releases the data that best proves they're lying, they lie some more, etc. Keeps them on their back foot. If there had been one data dump, the NSA folks would have been on the offensive for a month now.