Well, you have probably noticed that only five damage types are affected by the Absorb Elements spell: acid, cold, fire, lightning, or thunder damage. That leaves bludgeoning, force, necrotic, piercing, toxin, psychic, radiant, and slashing. There are reasons why these damage types are left out if you choose to think about them. First, there’s bludgeoning, piercing, and slashing. These two damage types have no magic behind them; it’s just your character getting hit in the face with a sword or a mace. No magic, just muscle, and there’s nothing to absorb. Psychic damage and toxin damage tend to affect the mind and the body quickly. If you are poisoned, there’s not much to resist, and you are often too busy fighting the poison to think about sending it back. It’s the same with physic damage, as that is mind to mind, and you can’t reliably channel that into a melee weapon strike. Radiant and necrotic are simply too powerful to be absorbed. While things like fire and cold are not only commonly found in nature, they are also things we can feel on our own. You can stand next to a fire and get burned or in a snowstorm and get cold. However, radiant and necrotic damage are powers that are attached to something higher. Absorbing the power of a good or evil deity without being prepared to take on that power can be detrimental, and you probably don’t have the focus or control necessary to focus that power into your weapon and strike back at your enemy with it. These are some of the reasons DM’s think up to explain away the rule restriction, and it’s certainly a lot better than saying: “Because that’s how the rules work!”