Why should best out of three be standard? What exactly do you mean by that? That the site enforces a best out of three? That wouldn't work, why would should somebody be forced to possibly play 3 games?. There are various, imo, valid reasons why one would leave and not give their opponent the opportunity of a remacth.
Perhaps somebody couldn't find a player of sufficient rating and played a game against somebody that was lower rated in order to bide time, leaving after winning is fine my be.
Perhaps the winner thought the loser wasn't a challenge, why should somebody have to play again against a weaker player if they want a challenge?
Perhaps the winner thought the loser took way too long to resign and doesn't want to play against such a player. I often dont allow rematches in such situations. I know its a player's right not to resign, they dont have to resign if they dont want to, however I also have the right not to play against such players if I dont want to.
Perhaps the loser was being rude. Why should somebody play against such players?
Perhaps does winner can't play anymore games/has to go, or perhaps the winner was waiting for a friend to come online to play them.
etc...
