NOTAMs are largely optional especially for things like making cropdusting passes in uncontrolled areas.
In this context the local pilots aren't out of compliance with any rules. The regulatory issue is that for almost all purposes human piloted craft have priority over remotely piloted craft, and there isn't a good way, currently, to communicate with pilots in the area.
Believe it or not, there are parts of the US, rural areas especially, where it is perfectly legal to fly an airplane without a radio or any other electronics.
All of these ag planes are operating under VFR, they can see each-other, largely they don't need to talk to each other, and don't need to know what exactly every plane in the vicinity is doing. It doesn't seem like it should work, but midair collisions between planes just aren't very common.
For planes, not filing an optional NOTAM for routine work is about as risky as not getting a police escort vehicle to go buy groceries. If we start allowing RC/autonomous cars on the roadway that place other drivers at risk, we might start wanting to file our grocery buying plans so we don't die. Or we would just say that you can't drive your RC car on the road when other road users are present.
In this context the local pilots aren't out of compliance with any rules. The regulatory issue is that for almost all purposes human piloted craft have priority over remotely piloted craft, and there isn't a good way, currently, to communicate with pilots in the area.
Believe it or not, there are parts of the US, rural areas especially, where it is perfectly legal to fly an airplane without a radio or any other electronics.