Really? In the US women needed their spouses written permission for many things even back to the 1970's. Combine that with early marriage age, I can see this being one reason.
Discussion
The early marriage age is actually a statistical anomaly from the 1950s. Women have typically married in their 20s, since we've kept records.
It really does have a root in who is willing to be a test subject. That's not all of it, but they've been trying to even out the sexes and they find it difficult to get women. Probably because they are risk averse.
Especially anything in pharmaceuticals or something else potentially dangerous. Or anything embarrassing.