>>96774437
>Except they did, just look at the XP value of monsters.
Which is adjusted by the Adventure Award.
All XP, including XP from killing monsters, is awarded at the end of the adventure, and there's a variable award that is suggested to be capped at the same value of the Monster XP, essentially providing DMs with the ability to double the gains from Monster XP, turning monster XP into a variable between x1.0-x2.0. Basically, it's a built in subjective modifier that adjusts the rate of XP, making Monster XP up to twice as valuable.

>A specific number of XP for monsters
That was modified by the DMs discretion, making it not specific. Even advancement in 1e is modified by a subjective performance score.