Because "Flatten a city" actually takes dramatically more scale than anyone has seen in decades.

40k Tons of bomb were dropped on Berlin in WW2. That's nearly all explosive payload too.

That's about equivalent to 80k modern cruise missile warheads.

The US has built less than 5000 Tomahawk missiles ever.

Russia has fired approximately 6000 missiles into Ukraine in the course of the war.

This is why the US still maintains a fleet of ancient "Bomb Truck" style bombers in the B52. Nothing compares to 100 B52s flying over a target for weeks. They allowed us to drop 20k tons of bombs on Vietnam and the surrounding countries. A horrific capability.

Gaza is a combination of Israel being utterly fucking insane and apparently desiring to terrorize people, and the fact that Gaza is super tiny.