To allow half the planet's population to also be competitive in sports. And often times, the style/technique slightly differs between them too.

In some sports you even have different weight classes. Rowing has 2, wrestling has 6 (olympic), boxing has 8-10 (olympic). The techniques there also differ slightly.

And there are other partitionings of the population too that restrict in who can participate in a competition. You have world championships, but you also have nationals. And regional competitions. And junior leagues. And school competitions.

Then there is also the paralympics.

You can find all that reasonable or ridiculous, but I'm not sure how that's related to doping.

Good question