It pressures the system in those cities or states, which is actual pressure to the system, just not direct pressure on the federal government. History shows you can mount pressure through local and state changes until it gets overwhelming support on a federal level.

You can make the argument there might be more effective or quicker solutions, but this is unquestionably one path toward it.

those doing the investigative work, away from public interaction (and possible abuse), are not the root of the problem there

They’re the root of privacy problems, which is a non-trivial issue for many of us.