Willingness to play.

It is similar to the problem with the neutron bomb. On the surface the idea of the neutron bomb (a bomb which kills humans via hard radiation but leaves infra intact) is not “worse” than a regular nuclear weapon. The dead die the same way and the living envy them. What CHANGES is the use calculus. I might not want to bomb an industrial valley if doing so destroys the thing I am trying to capture. However, if I have a bomb which kills the people living there and spares the factory, I might pull the trigger.

Similarly, it is cheap (relatively) to indiscriminately launch weapons at a distant place. It is extraordinarily expensive to send human troops in. They need food, water, and generally have families that expect some of them to come home. If putting a rifle on an autonomous vehicle works, then a ground invasion becomes cheaper.