Defenders were quite keen not to be killed, and urban warfare is very unpredictable. Commanders are also usually keen to keep the 'artistry' in war. If defended, an attacker would usually employ maximum firepower rather than high-casualty, house-to-house fighting where everything favoured the defender.

So for prolonged house-to-house fighting to occur, there usually had to be some tactical or political reason. Even thoroughly blasted towns had to be taken by infantry if they were defended. If a town could avoid being encircled, then usually there would be salient positions within the city that would be defended: the Tractor Factory at Stalingrad, the town square in Kharkov, the industrial area of Caen, and the Old Town of Aarchen.

To dig in and defend a city to the last was suicidal: the city could hold out, but would be surrounded after a time, and thus escape impossible. And if the defence was prolonged after being surrounded, the attackers were far less likely to take prisoners. So defenders usually had an incentive to give up cities even if they were defensible (Mogilev and Bobruisk, Tarnopol, Breslau, Manila, Mandalay.

A good example is the Canadian army's battle to take Ortona in late 1943. The town had a prewar population of around 10,000, yet the tight streets and most buildings being adjacent let to the use of lots of methods we would generally consider to be part of urban combat. To move up streets soldiers would enter a house and blow a hole in the wall to get to next house without being exposed to enemy fire.

What decided whats sort of tactics were used would have relied heavily on the geography and architecture of the town. The small and densely build towns of France, Belgium, the Netherlands, and Italy would have lent them selves much more easily to the use of what we see as stereotypical urban combat tactics.