Ixixly - I shall try to answer your questions, and thanks for taking an interest in a relatively obscure topic.
The label on a chemical drum is a legal document. It must be complied with. Essentially it is illegal to open that drum until that label is checked.
That label stipulates all the parameters acceptable to the regulator for the application for reasons of safety.
It will specify a droplet range required for aerial application. Say 300 + microns.(think drizzle/light rain) for reasons of drift mitigation.
For the product to work, a certain amount of droplets are required per square cm on the target.
Lets say insecticide so 20 droplets per square cm.
This will require, and the label will specify, a total spray volume in the order of 30 liters per hectare. (this varies between products)
Aircraft are designed around these specs.
A drone on the other hand, with the reduced capacity, will distribute in the order of 1 or 2 liters per hectare (or less) at maybe 80 microns(or less) (think fly spray aerosol) to attempt to achieve the 20 droplets per square cm.
This is contrary to the label instructions, read illegal.
The situation is worse for herbicides, generally requiring higher volumes and more droplets per square cm.
There is work going on attempting to change labels to legalise drone application.
In short, big droplets require big volumes. Drones don't do big volumes at this point as they do not have the necessary capacity.
Regarding third party risk. Operations where a "what if" regarding safety of others are not entertained.
The treatment area is inspected thoroughly prior to and rechecked during the application, including the area downwind.
There is not much that cannot be seen approaching the treatment area from up at 300 feet when turning at each end of the field.
This happens at intervals of tens of seconds.
Spent plenty of time holding at 300 ft organising the removal of persons from or near the treatment area. Sometimes, they just turn up for a look and stop several aircraft working.
Regarding insurance, sure drones are insured. How about the pesticide application element? That is a separate element.
Drone tech is clever, very clever. Unconvinced it is suitable for the safe application of pesticides.
However, some parts of the world do not have the same concerns regarding safety and legality.
And, in some parts of the world it is probably somehow cost effective to have ten drones, ten operators and ten support vehicles turn up and work all night to spray a field.