Why does mana keep getting more and more scarce?

I know the base idea and everything, and i certainly don't want everyone spamming spells all day. Before making mana regen even more rare, it's already an issue on champs with very low mana costs to begin with, so now it's going to be even more skewed. I don't think anyone has fun deciding whether to b solely because they have no mana, or to stay and try and keep up on xp and gold but be nearly worthless if a fight breaks out. Lanes are aggressive pretty often, and when the enemy is charging in and throwing abilities left and right, you have to use mana to respond. I get the underlying idea of mana and pacing yourself, but the fact of the matter is, if the enemy doesn't have to pace themselves, you're going to lose farm, fights, and quite possibly even the lane simply because you don't have mana to fight. If you take time out of your build to buy a mana item when your opponent doesn't need to worry about it, you're sacrificing so much power that it doesn't even matter that you can keep up with abilities anymore, they hit so much harder/tank so much more that you might as well have gone something else.

With energy champs being back to full capability within seconds of leaving combat(on top of being rather popular right now), and some champs like karma not needing to worry about mana much in the first place, this feels like it's going to push out the mana hungry characters even more. Junglers are going to feel it too since they can no longer get a chunk of mana from smiting blue. Mana hungry junglers are going to have to take an even tougher hit if they want to give blue to mid like usual. If they aren't a champ that can use echoes(not to mention that finishing that item isn't enough for the heavier mana users), it's going to make a significant difference in how often they can gank, along with very likely reduced clear speeds. I love seeing a bunch of new changes, but when they start shoehorning champs into or out of roles, they start feeling more like sideways movement instead of forward progress.

Edit: I feel like I failed to properly draw attention to how hard this hits junglers. This is my main concern with mana right now, though I do still feel like it's in such a strange spot overall that it removes certain champs from viability in all but the most favorable of matchups.