The Torah is not a social benefit document. That is for the Rabanan or a present king. The Halacha of a woman not remarrying within three months is, in fact, Derabanan.
If you want discuss how the Mitzvos match social needs, philosophical reasoning or the Shiur Koma, that is fine. You can add reasons, and this has been done. But you must always remember what David Hamelech said, Lechal Tichla Ra’isi Ketz; Rechava Mitzvas’cha Me’od.