He’s already abandoned Russian civilians in the Kursk region, and the concrete bunkers are being built for Russian soldiers, not civilians. Nuking Russian territory for a war he proudly started would not go over well, because all of the border regions would start shitting themselves over the thought of Ukraine invading and them getting nuked. If Ukraine starts sending troops into other Russian oblasts, those oblasts are liable to declare themselves independent in hopes of the international community preventing them from getting nuked.
I also think the US/EU/Japan and others would sanction anybody doing business with Russia just as hard as we are Russia, which would turbofuck China and/or India. As it stands, China is easing back on Russian imports because something has them spooked about further sanctions.
No guesses as to how the current situation plays out, but the fact that we are two weeks in and Russia hasn’t been able to gain any real victories in Kursk speaks more about the Russian manpower situation than any daily body counts we see.
And yeah all of those drones sent at Moscow may have been shot down, but they are still using up precious Russian AD and forcing the Russians to being more AD out of Ukraine and the border areas.