What makes you say that? I can't really think of how it could be considered rational from that perspective GirlWritesWhat had a video where she explained it pretty well. Unfortunately with her I can never remember what video it actually was. The gist of it was (if I remember correctly) that women are biologically more choosy when it comes to mates, because they bear greater biological risk when reproducing. As a result if she "gets around" she's more likely to become pregnant more often, and populate a community with many kids who may not be well cared for, etc. Once again this is all from an evolutionary context. It doesn't apply so much in modern society. This video explains it a lot more as well: