Why does this still happen?

Just recently I played a game as Illaoi, and in champ select 4/5 had already called our roles. We had a Yi jg, Jax mid, Cho supp, and me as Illaoi top; however, one player decided he wanted jg and locked in Rengar with smite. When we told him Yi was jg (everyone was locked in) and that he would have to go bot lane, he quit. Before the game even started, in champ select. And the game went ahead anyway. Why does this happen? It's in champ select when he left, so the game could've disconnected us and put us back in queue; but no, we had to start with a major disadvantage. We actually were doing very well, but the pushing changes did us over; please Riot, just fix this.