The classic rude children's rhyme is only half right. Many of us don't have any balls (or ovaries) at all! Why leave your precious germline cells where they can be mutated into uselessness by the solar wind when you can store them safely in a lead freezer on the station? Out in the dark any number of disasters can befall you, and with asteroid populations at the lower end of long term viability, there's no room for a freak shuttle accident to cut into the available gene pool.
You only have to save one, but plenty of people just get both removed when they come of age and are ready for outside work; the vagaries of an endocrine system are another uncontrolled variable no one wants. Hormones are easy enough for any ship to make.