Guns don't scale like drones. No matter how many guns you own, you can only shoot two at a time, and only one if you care about aim.

Building an autonomous drone swarm capable of nuclear-weapon-tier kill count is far easier than building a nuclear weapon. We already know how dangerous military drones are, and those are still mostly bottlenecked by relying on human-powered target identification. Building drones to indiscriminately kill unarmored civilians is an easier task.

But the tooling required for guns and rifling in particular is pretty hard to come by, whereas the tooling required to assemble a DIY drone is basically indistinguishable from R/C hobby equipment. You can (try) to regulate where/who/how/when can fly a drone, but regulating drone building seems almost impossible to me.

You can setup a machine gun on a Remote Weapon Station and control it via the internet. You could have agents as machine gunners. Same with rocket launchers.

We are literally seeing the large scale use of robotic weapons platforms AT SCALE.

Machine guns create a storm of ballistic objects, and have been doing so for over 100 years. Large scale murder isn't new. We just have systems that have cameras that make it easy to put the footage online now.