Because if the rules are made clear that a category is female only, why would anyone need to be 'outed' if there is an open category and females who choose to compete in the open category are doing so?
Having a 'special women's' category would attract who? Any person who doesn't qualify as a 'biological woman' in your words ie. Any person who is not female. Why would any female person compete in a category where a male person is going to enter and is likely to win? And we all saw how a trans category was set up and ignored in the recent swimming event.
ALL males who compete in a female category which has been set up to allow female people a chance to compete fairly are 'cheating'. Just because they may not be competing against the rules, if they are there, they are a potential harm for women and girls. And the harms are numerous, from physical harm through to causing a woman or girl to be excluded because that male took a place where a woman or girl could be, or because female people do not want to compete with or against a male person.
Again, you have tried to position yourself as some kind of middle ground / compromise advocate when you seem to have very little knowledge about how sport's categories work, what the intention of those categories are and what your solutions mean in practice.
Tell us, what other sport categories are you happy to allow the category boundaries to be breached just because someone identifies as something they are not. Seriously, you are arguing for cross category entry for athletes where no athlete has been permitted to enter before. Why are these males able to do this when no one else is?
Why can’t a 25 year old compete in the Masters in the other 75 year old category if they identify as a 75 year old?
Why can’t that 25 year old compete in the under 12 year old category if they identify as an under 12?
Why can’t a fully sighted person compete in a category for the visually impaired if they identify as visually impaired?
Why can’t a heavy weight compete in a lighter weight if they identify as that lighter weight?
Why can’t a black belt compete with a beginner if they identify as a beginner?
Why can’t a professional compete as an amateur if they say they are?
If you have ANY category that is labelled or 'women', 'girls', or 'female', then that category is single sex. There is no logic for having two categories and expecting any female athlete to compete in the 'special women's' category. Your solution is make believe and unworkable. And it gives all male people just another opportunity to win and ignores the needs of female athletes.