The objective of war is to kill people and break their things.
In the case of the infrastructure bombing late in the war, it was also to stop things from moving or functioning.
Troops could not get from one part of the country to where the allied advances were being made. Fuel, food, ammunition, vehicles, and other supplies could not get to the troops who needed them.
Had the allies began this sort of bombing right after D Day the war in Europe might have been greatly shortened.