It's almost certainly more complicated than this. The NSA is scary, but it's also not a revenue producing part of the government, and therefore it must justify its existence in the budget every year. Lawmakers therefore must be doing some sort of cost/benefit analysis and have determined (perhaps by looking at the NSA's secret output) that the cost is worth it.

tl;dr: If Congress wanted to chastise the NSA, all they have to do is not fund it.