@Riot Why are mages the only champs that have to manage mana late game?

I just want to know why you decided that mages are the only class of champions that have to manage mana even in late game?

About a month ago you explained that Darius had mana so he wouldn't just spam his spells on CD early game (which is reasonable for all classes) but that late game his gameplay is supposed to be more about "target choice and positioning". Both of which mages still have to focus on, while apparently simultaneously managing their mana.

I'd understand if you don't want ranged characters having access to infinite poke, but you gave AD Casters access to essence reaver which allows them to do the same thing. And mages already trade defenses and mobility for the ability to do ranged damage, so why do they also have to worry about mana?

Even if the new items give mages enough mana to team fight and then siege (if they used reasonable amounts of mana), why are they the only ones forced to back afterwards?

I just want to know why literally every other champion is either manaless, has a mana pool that greatly outscales mana costs, or has access to useful items that effectively make mana semi-infinite or infinite (Essence Reaver for AD casters, mp5 items for supports).