Nukes do way to much damage, there is no point on bombing a city if you can't have it later, a nuke would not only level most of the city but also leave it barren and irradiated for quite some time, it's not in the best interest for those in power.

It would actually be better to make a bunch of killbots that clean up after themselves, in this case you can eat the cake and have it too. You can keep the city and it's relics instead rebuilding it.

War isn't about just killing, it's about taking something wether it's freedom, equality, treasures or just land.

Also Asimov cool books an smart fellow, but seriously his rules are like 100 years old when robots couldn't even perform nowhere near how they perform now. We can make the illusion that the robot actually thinks now, with things like godbot or whatever, think 20 years from how much improvement do you think there is going to be?