Soldiers are powered by eating organics, potentially very light weight organics rehydrated with locally available water. They can carry several days worth of rations and be operationally effective for nearly 24/7 of those days.
There is no robot on the planet yet which has a battery that will last on 'standby' for multiple days, allow it to engage in active service for several hours each of those days. The weight kills you. It slows you down.
Two technologies "win" in the military space. Just enough tech and weight to increase down range lethality over the existing system, and tech which doesn't have to be carried so can be called in remotely.