In a FFA game, 2 players are guaranteed to get nothing which is identical to a personal loot game.
A character can wait in town twiddling their thumbs and wait for the others to entirely clear a map. In a personal loot game , if the town character goes to the cleared area, they get no loot whatsoever. In a FFA game in D2, they can grab all the uncollected loot in the cleared ma without any risk.
Therefore, FFA promotes the freeloader just chilling in town waiting for others to do the work where that can get gear after the work is done. Personal loot at least requires you to be in close proximity and potentially harms way,