According to Why the Allies Won by Richard Overy, strategic bombing proved to be decisive element in the Allied victory.
I am aware that there is a considerable debate over the effectiveness of strategic bombing; however, this question concerns the Luftwaffe’s terror bombing of 1940 and why it was or is considered less effective against civilian morale than the later Allied bombing of Germany, for example.
Was it a matter of sheer volume of attacks, bombing tactics, timing, or a fundamental difference in implementation or motive that made the Allied bombing campaigns far more effective at destroying countries’ abilities and will to wage war?
Does this question assume facts not in evidence?
The bombing didn't break axis morale. The bombing was decisive because it imposed enormous costs on germany. By 1944, the defense of the reich was consuming something like 1/3 of all the ammunition germany produced, virtually the entire air force, and most of the artillery pieces. Every plane and gun shooting at allied bombers was one that wasn't shooting up Allied tanks and soldiers as they pressed ever closer. German air superiority was absolutely decisive for them earlier in the war, and the bombing campaign destroyed it. Even before you take into account disruptions to production that bombing caused, the loss of efficiency from the need to de-centralize production, and the sheer cost of rebuilding after the destruction, it's hard to overstate how immense those costs were.