This Uber gender option is about safety for women.
Some women are afraid of male Uber drivers stalking them and learning of their home address. To avoid that, they have to follow "best practice" hacks such as entering a decoy address of a nearby intersection for pickup and dropoff. This makes it more inconvenient but a little harder for Uber drivers to figure out exactly where they live.
Allowing for "female-only" drivers may help passengers avoid the cloak-and-dagger workarounds.