I don’t know what or if there are any cannon explanations, but I always had understood force as well… force. Bludgeoning, piercing, slashing are damage amplifiers that make do with limited force. But if you trying to damage say, a rock, they are basically irrelevant. But you put a rock in a hydrolic press and apply a enough force, and boom it cannot withstand. So being hit by an eldritch blast is less like being shot and more like being hit with a high pressure oil leak.