Men are stronger, faster, have more dense bones, have bigger lungs, bigger hands, etc, etc, etc. Men and women are different in hundreds of ways it's not just 'lean body mass'. Men are better at sports than women. Do you even live in reality? Have you ever completed in anything in your life?
For what conceivable reason would you want to recreate the male and female division using a dozen or more proxies for sex instead of just using sex, to wind up with people being placed into the same buckets they would have been if you just went by sex in the first place? This seems ideologically motivated.
The controversy in these comments answers that question nicely. It seems likely that such a change would obviate these edge cases, though they may introduce their own; that seems worthy of consideration.
Really, the question seems better turned around: why use a known bad proxy for physical ability when another one might be better?
Those divisions already exists. Most sports have different leagues. There are international leagues, national leagues, regional leagues, all the way down to hobby leagues or beer leagues. If we assign everyone into a league independent of gender, the highest leagues (the most popular and most lucrative ones) will be exclusively men and women will only be present in the lower leagues. No one can want this outcome.
And then you get a situation with as many divisions as there are people and everyone get a gold medal, everyone is a winner. The true woke paradise.
Fortunately, most people don't like to live in this hell and are against clear attempts to destroy women's sports by the clueless and/or purposefully malicious activists.
Good lord. Absolutely nobody is going to watch boxing divisions based on lung size and bone density.
Did you actually think that lean mass would be a sensible way to separate divisions in a gender neutral fashion? That would, again, just result in women being unable to compete professionally in virtually any sport. They would be relegated to Division N, for some very large value of N. Competing alongside multitudes of biologically male amateurs, where nobody cares and nobody pays to watch. To even entertain this idea betrays a total lack of understanding of the matter at hand.
Right now you are acting like Elon Musk storming into the government and having 20 year olds cut everybody's budget. You may think you're coming in with fresh outsider perspective and an open minded way to look at things and improve them, but everyone actually involved in the domain can see a trainwreck in progress. It's not a good look.
I am quite certain it's not your intention, but you're really coming across as someone who hates women's sports, and doesn't want them to exist. On behalf of my wife and sister and a lot of the women I've known in a lifetime of playing sports - kindly keep your awful ideas to yourself. Women fought tooth and nail for the right to have their own professional sporting opportunities. Don't you dare try to take it away from them.