Because this particular military spy organisation is being deployed by the US government against its own citizens, en masse, as an end-around well-established due process and constitutional protections that require individualised suspicion of wrongdoing. It also represents a giant exfiltration target for other state actors, like those who breached OPM. NSA hurts the security of Americans under the guise of preventing foreign terrorism, which happens to pose a risk comparable to lightning strikes.

So you're telling me there's no evidence that the NSA has committed call logs of every US Verizon subscriber to their own persistent storage for later inspection? No evidence that NSA intercepted inter-datacenter transfers of American companies, who were housing the personal data of Americans? No evidence that Americans have been swept up in overly-broad "one foreign end" wiretaps? All of the weakdh.org people are crazy? That well-documented room in the AT&T building in San Francisco was just a big misunderstanding?

I would not do it if I was in their position. I'm a US citizen, so I believe in upholding the constitution, which includes a prohibition on unreasonable search and seizure. Whatever the lawyers and judges have made "unreasonable" out to be, NSA dragnet surveillance is way beyond "reasonable" and on into "police state" territory.

Also, I'm not a pervert who gets kicks from listening to others' conversations. They apparently are.

The only reasonable assumption I can come up with for not cracking the stock primes would be expense and inability to execute on a plan. Otherwise, it makes perfect sense to crack them. And, talk about fun and interesting work!