You can't oppress people with artillery.

You need to get close to them to check their identity, their Covid passes, or whatever. You need to get close to confiscate contraband. You need to get close to prevent them from organizing and assembling, and so on.

Of course with nuclear bombs and F-16s you can blow everything to bits, but that's not how governments typically oppress people. You generally don't want to exterminate your tax base, you just want them to have the "right" opinions and beliefs.