Why is it that Essence Reaver only good on like 1 Champion?

Edit: Forgot about Sivir, but still

I do not understand why Essence Reaver grants 1.5% max mana on hit, as opposed to % of damage dealt considering casters other than Lucian don't attack very fast.

Other than Lucian, who else in this game

• Is mana hungry
• Crits
• Actually attacks fast enough for ER to be relevant early/mid game
• Has a kit that isn't gimped by going ER instead of an AS/Crit item and only having 40% crit?

Might be the only contenders, but Jhin doesn't have mana problems and MF gets played once every century.

IMO the old Essence Reaver was 'better' in that: it worked on every AD champion, the stats were just pretty lackluster so very few people built it over BT/BoRK at the time which were strong AF.