I played goalie on my high school soccer team in my junior and senior years. The first two games of my junior season were against schools that didn't have football teams, so the jocks were all on the soccer team. My school had a football team -- a good one -- so we soccer players were not an integral part of the jock brotherhood.
My first game was a loss by a score of something like 16 - 0. The second game was something like 12 - 0 and featured me having a goal scored against me by one of my own defensive backs. I wouldn't have wanted there to be a mercy rule in effect. Once that gets invoked, the poorer team has no benchmark for how good or how bad they are, because the other team isn't allowed to play to the limit of their ability. Anything the losers accomplish from that point forward is irrelevant, because it's accomplished in an artificially rigged setting.