I think you missed the point, giving a link explaining why they want to run a female only event doesn't answer the poster's question of why it isn't dealt with by the authorities.
I presume it is legal but why it is isn't explained in your link.
I edited my post a bit more after you quoted it. Presumably it is legal because the reasons they have given are quite reasonable, based on factual information (in terms of their fundraising amounts) and because they are not based around prejudiced views.