The problem is that doubles is played by partners. Two people simply should not stand on the same side of the net. Part of the reason tennis is so compelling is that a player has to confront the fact that she’s out there by herself. A doubles player does not. Consider the Bryan brothers, the best doubles team playing, one of the best teams ever. One is left handed, one right; one is Bob and one is Mike. Otherwise, they pretty much share a life. The zygote did not fully split. They always have each other. They are never, ever alone.
(I have no explanation for the sudden quoting of tennis commentary. I don’t even watch tennis.)