I mean... yeah, that’s a definite possibility. If a lunatic has access to explosives, there’s an infinite number of ways they could do that.
The hard part is that there is no effective way to regulate anything in the supply chain involved except for the explosives themselves. Everything else is super commoditized at this point and, other than the props, very multi-purpose. The first significant hexcopter I built used a BeagleBone Blue for processing, generic ESCs and BLDCs for the motors, and an aluminum frame that I cut out of aluminum tubes from Home Depot. Max takeoff weight was 55lb, because that’s the heaviest it could legally take off with. This was 7 years ago.
If one is a lunatic, there are easy to find recipes for making bulk (albeit dangerous to be around) explosives.
one thing in societies favor though - sufficiently unstable lunatics tend to self delete themselves in various ways by being unstable lunatics. few tend to be in the “sweet” spot of dangerous lunatics who are stable and focused enough to follow through successfully with a dangerous plan. thankfully.
For example - most people who could synthesize multi-kilo quantities of TATP without blowing themselves up and successfully build a DIY drone to carry it have better and more productive things to do with their lives. at least in the west.