Why can't Riot just nerf AoE damage to creeps

Why can't they adjust mana costs based on problem cases instead of just blanket destroying mages. Why are you so lazy. Wtf do you even do every 2 weeks? Take 5 damage on Janna W, swap Ahri's 2 passives around and call it a rework, revert another one of Repetoir's reworks? Like what the fuck do you do for 8 hours.