Scaling vs Amount Behind?

At what point do people give up on the idea of "well scale into late game" not matter anymore? I have had a bunch of games recently where I have had people get so far behind in a game, but say "don't worry well scale" as if that would make the fact that the other team had almost 40 kills at 15 minutes pointless. I understand the scaling thing, but why do people seem to believe it regardless of the situation? If they are taking nexus towers by 20 minutes, with over double our kills, 3 levels up and full builds there is no more "scaling to match them", the game is over. Do people tell themselves that to feel better? Can someone explain it to me.