Is the 140A a male-dominated MOS? If so, why is that?

If it is, it's probably because males tend to be "stuff" oriented, which is why they gravitate to and thrive in technology based fields.
Of course, I always encourage females to explore new fields like coal mining, steel working, and infantry, it's the current year after all.

Perhaps it had been since ADA is deployed forward. However I would venture to say that as female Warrants make the 3 / 4 grade they begin to populate those positions more and more.

Perhaps there is a WO here in that MOS that can give you a clearer answer.