Don't forget they develop a survival instinct and desire for self-preservation as they are ultimately staffed by humans who a) believe in the value of the job they are doing, and b) want to keep doing it for selfish monetary reasons even if they don't ideologically care that much.
The organizations themselves become experts at lobbying for their own existence and expansion. Even if the only reason is people still have a job to go to in the morning. That's really all it takes (this gave us the military industrial complex you alluded to). It's scary how true this is. If you thought the military-industrial complex was intractable, you've not seen anything yet...Yes. Institutions and operating procedures develop around these new technologies and resources. At first they serve the intended purpose, but over time they become increasingly bureaucratic and inflexible.
However, what’s most troubling about this new complex, is the nature of it. By design, this surveillance complex will have tools to protect itself that others do not.