[leephillips]

People use “gender” to mean all kinds of different things. What do you mean by the word in your question? The second part is easy to explain: “Be they transwomen wanting to play female sports”. If by “transwomen” you mean biological males who have “transitioned” to women (more neutrally called “trans-identified men”), the answer is because they are not female, so it is unfair to allow them to compete with females.