Let me spell it out for you slowly: why do we segregate the sexes in the Olympics? Can you handle that? take a deep breath and try.
As for your dodge: yes indeed weight lifting, boxing, have weight classes - why not let all in those weight divisions, men and women, vie for qualification and then if they make the cut compete in the games?
I bet you won't answer.
Why do we have weight classes for boxing or for MMA? Because otherwise we would never see a champion like Georges St. Pierre compete as a champion. We would never have seen Sugar Ray Leonard compete as a champion - and the world would be a much poorer place.
Maybe in idiot land only heavy weight boxers need to compete - and anyone who is physically unable to match blows with a 230 lb 6'3” bruiser should just stay on the couch.
Lightweight boxing is almost a different sport than the heavyweights - much more exciting IMHO than two big slabs of beef leaning on each other.
Luckily we don't live in idiotland - we live in a world where a man or a woman is not limited by their physicality and can train to compete to the best of their ability at a championship level.
Why? Was the answer you wanted ‘because women are not as strong and as fast as a man.’? That is an idiotic answer. A welterweight boxer is not as strong as a heavyweight boxer. Does this mean they should just stay home?