So all the defense community was raised on SIGINT, and anything seen as a curb on this - technical or legal, they will probably view it as some sort of existential threat. They would then fight tooth and nail to block any sort of reform. And the military industrial complex has quite a lot of legislative muscle....
The rise of technology, both its widespread use by the public and the ability to capture it by agencies, had made SIGINT seem much more attractive in the couple of decades prior to 9/11.
So, yes, agencies had become over-reliant on SIGINT over HUMINT, but for understandable reasons with the benefit of hindsight. Currently, they certainly don't view it as an existential threat and all agencies are working to re-establish HUMINT capability, the opposite of trying to block it. The trouble is that it is hard, really hard work.
They like to toss words like "Terrorism" around like frisbees hoping someone will catch it and toss it to someone else, however I personally think we can assume that direct diplomacy is dead. SIGINT is more consistent and dependable than engaging another nation's diplomatic apparatus, and all nations are clamoring for their own monitoring solution.
It's a new baseline measurement of international political power -- the cost is so low that it's foolish not to get it.