Why can they not use firebombing and other conventional munitions? If they can deliver a nuke surely they can deliver a conventional warhead. That is enough to level an urban area as we see in Gaza.

If you level a city you just removed 95% of the reason for trying to capture that city.

Spending untold billions of dollars and tens of thousands of lives for a pile of ash would never pay itself off.

The reason for Putin at this point is more reputational than inherent value of whatever lies in Ukrainian city. I fully expect Putin would nuke the ever living shit out of Ukraine into a glass worthless pile of rubble if he thought he could get away with it.

Israel levelled Gaza after capturing the area, with artillery and with air strikes.

Russia hasn’t captured Kiev, their artillery can’t reach that far and they don’t have air superiority - Russia hardly has an airforce anymore.

Also worth remembering that Gaza is effectively an island when it comes to logistics. This made it easy for Israel to cut off food/medicine/fuel. Essentially medieval siege warfare transferred to the present day.

Russia fires conventional warheads into Kiev all the time. Thousands of civilians have been killed and injured. The city survives.

Buildings in Kiev aren't made out of wood. Firebombs would do very little damage.

Russia cannot fly a plane into Ukrainian airspace. They barely even fly over Russia's side of the line right now.

They toss bomb from miles back.

Flying conventional bombers over enemy cities requires the ability to replace most of your bombers per year, or air supremacy, neither of which Russia has even a hope of doing.

WW2 was industrialized the likes of which nobody has ever seen again.

Because Russia doesn’t actually have the resources to do this at the scale required. Russia is also not trying to obliterate Ukraine. They want to take over a real economy, not a wasteland.

At this point, I think they would take the wasteland "win" if they had to. But they really don't have the resources to do carpet bombing or something like that. Just lobby pot-shots.