This comment nails it: the point is to keep the logistics train simple. An antidrone platform is much more useful if it uses the same 5.56 as the service rifle

This comment nails it: the point is to keep the logistics train simple. An antidrone platform is much more useful if it uses the same 5.56 as the service rifle and squad machine guns. When you can just improve the software/optics, well, why not?