The problem is that every class benefits from a long rest. Everything resets on them. HP, spells, class features, etc. However, short rests were specific to only certain classes (and races). Fighter, monk, and warlock all had important parts of their kit requiring short rests. Cleric, druid, and bard (after 5th level) got use out of them, but the ability was more situational and they had regular spellcasting to fall back on. Wizards, sorcerers and barbarians got almost no benefit, and the rogue had no resources to build so they only ever rest to heal.