They aren't divided by "gender" as a socially-defined category, they are divided by a biological category of sex. That is the reason why there have been sex tests in elite sport and why athletes such as Semenya have been identified as DSD male, because they have tested for male levels of testosterone. It is why there is this ongoing debate about whether biological males who identify as female should be able to compete against women. If there was no objective requirement that being female is a biological fact and not simply what some one thinks or says they are then none of this would be an issue.