Why is this game so unfun?

Why is every lane decided by the first mistake someone makes? Why does every goddamn champion hit like an atom bomb and dash around like a bullet train? Why is every champion also so infuriatingly annoying to play against it gives you a headache? Why does every champion have almost no diversity and a single build path? Why do they blatantly leave popular champions overpowered and ignore the rest? Why is the only genuinely fun part of this game when you win?

and more importantly Why in the everloving shit am I still playing? I keep hoping it will get better, but it never does. Games shouldn't be only fun for the last five seconds of their forty minute painful existence.