Also, why do they dismiss asking ISS staff to participate in studies? Bodily autonomy doesn’t mean you can’t ask someone to conduct … uh… research with you. It just means you have to respect it they say no. Astronauts seem like the types who wouldn’t mind putting in a little extra effort for… science.

Too many other introduced variables? Microgravity has a lot of other systemic effects on the astronauts that might affect sperm motility, even before effects to the sperm themselves. Or just individual variation/genetics on the part of the astronauts themselves.

They wouldn't be able to get a sperm sample that wasn't affected by microgravity from the astronauts to begin with.