Because of the faction of folks who view hit points as a physical wounding mechanic. An evoker's fireball does damage on a miss because you still got singed from the flames but you avoided the brunt of the attack.
I think that "damage on a miss" could actually be sold with the right presentation. Calling it "damage on a miss" already sets up people to knock it down. For example, give the Fighter a special ability at 3rd level which is called something like "Weapon Expertise". The text of the rule is something like "You are so highly trained with fighting with your weapons of choice that you rarely actually miss your target when using them - if you do not beat the opponent's AC but also do not roll a 1 you are able to achieve a glancing blow on the target doing Str bonus + proficiency bonus damage. A 1 always misses." Or something to that effect. It respects the fiction for those who want hp to be meat and also works with the vision of the fighter as a martial weapon master.