This article seems to focus on the United States, where there really isn't an imbalance.
Edit-another pet theory is a changing climate. Cultures in drier climates tend to be more sexually conservative. A large portion of the US has been in drought conditions for decades
Granted, as has been pointed out by the parent comment to yours, this study is referring to the US specifically, where there are more women than men in 40 states (https://www.statista.com/statistics/301946/us-population-mal...)