This is a distortion of a real phenomenon which occurs in humans and other species, but “hierarchy” probably isn’t involved here, and it’s not specific to women.
To use a highly simplified example, let’s say that there are three men and three women, all hetero, who know each other very well and aren’t much involved with anyone else. None have any standout traits which might make some of them more interesting to certain others, and all would be reasonably happy with any of the others of the opposite sex. This may lead to a situation where everyone wants to date, but no one’s sure who to go for. Regardless, at some point a couple semi-randomly forms out of this group and dates for awhile. It goes well. And then, one of the couple needs to move far away so they break up amicably, or dies, or otherwise becomes permanently available.
What’s likely, but far from guaranteed, to happen within the next few months: The remaining member of the former couple will have the remaining two people of the opposite sex fighting over them. Perhaps out of envy (“I want what they had”) perhaps out of proven reliability (“they were a good relationship partner, I don’t know about the others”) or even out of curiosity (“he/she must have seen something special in them, I want to know what it is”). Regardless of the individual motivation, there’s a subtle instinctive bias going on here - it probably has a name, but I don’t remember what it is. It can result in a pretty unfair situation, but life isn’t always fair in far more ways than that.