I think it's because in other games you don't really hurt the experience of the other players by leaving when you're losing (or at least, the effect is minimized). In Battlefield or CoD, if you are getting creamed and you log, no one will notice. In Rocket League, the game will replace you with an NPC and the winning team still gets the rewards of victory. In 1v1 sports games, the logger gets penalized and there are ranks and reputations so eventually players that don't quit are more likely to get paired with other players.
Thus, as others have pointed out, players that don't read the forums may not know that their personal loss is part of the experience and, to the larger point, more directly a part of their attacker's gain.
Perhaps on Xbox there's a larger percentage of Elite players falling into the CoD/Battlefield/Madden multiplayer mentality (not saying it derisively, just stating as a hypothesis on the numbers based on anecdotal personal experience) than on the PC, and PC-side of Elite likely has have a larger DayZ/Eve crowd that is into and understands unforgiving PvP universes.