The most plausible scenario (and the one that is consistent with later highly stratified societies) is that they just could not marry locally due to status diff

The most plausible scenario (and the one that is consistent with later highly stratified societies) is that they just could not marry locally due to status differential to all local males outside of the family. That's all the social construct you need to match the observation. But the article paints that as an act of sending away, when a more passive approach is not only just as plausible, if not more, but also supported by the observation of males that did a significant amount of traveling before settling down back home.