This is a point worth exploring. There is a part of the world, the Eurasian steppe, where folks still practice nomadic herding precisely because the geography discourages trying to defend stationary encampments. Today, cities dot the North American plains, another region traditionally inhabited by nomads; this is because of strong social institutions. If those social institutions fail, then the nomadic way of life will become preferable again.

I wonder whether these bunker-builders would get more bang for their buck if they were to build inside a city instead of outside. Investments in infrastructure around them could improve security at a structural level. (A distant relative thread notes that bunkers could not possibly have full hospital service.) A castle does not have just a keep, but an entire town inside its walls, or else it could not support its keep.

Well if others know there's a bunker there then you're already doing something wrong

100 rounds of ammunition take very little storage space.

That's why you have a replica bunker just below it, just in case. Gotta stay antifragile.

Or have a replica bunker next to it but it's rigged to blow a dirty nuke and trigger an apocalypse-upon-apocalypse in case the zombie horde comes knocking

(I'm not seriously suggesting this)

It’s bunkers all the way down.

Or a shoddy fake bunker just above it as a decoy.