The difference is the business structure. Women's only gyms are operated as private clubs, and must follow a very strict set of laws. Uber is a public accommod

The difference is the business structure. Women's only gyms are operated as private clubs, and must follow a very strict set of laws. Uber is a public accommodation. It cannot discriminate based on sex. If someone wanted to start a private club where women joined to drive and be driven in a not-for-profit way, that would also be legal.