A model of immersion

[Tanarii]

I'm coming to the conclusion that it's because it was (relatively) new. HP is long-standing and in just about every video game property and lots of popular culture. And the idea of taking massive hits and keeping fighting with no (apparent at the time) impairment is actually a staple of Action Hero and Super Hero movies and media--the scale changes, but the idea is constant. And that's an idea that ties into HP.

AEDU was a major change for D&D from 3e, and the "who moved my cheese" phenomenon kicked in hard.

It's sad too, because it was a genuine flash of genius break-through for martial and other formerly "I attack" classes to get AEDU powers.

5e retained a vestige of that. One Fighter subclass (Battlemaster) and one class (Monks) inherited the feeling with their Encounter 'Powers'. And There's a reason EKs/ATs are hugely popular fighter and rogue (respectively) subclasses. They open up new and exciting at-will and daily 'Powers'. Also Paladins and Rangers are generally liked for their daily 'Powers' (although Rangers get bashed for other reasons). Even Barbarians have daily Rage resources. 5e pulled it off, but it just doesn't feel the same. Mainly, all those classes are playable because combat was so simplified that it's lightning fast in comparison, and also designated to work with the fog-of-war / imprecision of Theatre of the Mind, so genuine battlemat style tactical play isn't particularly important.