It's very simple - women have lost the shame of being single mommies, either via being knocked up in or outside of marriage by a man that had no intention of staying with her, or by flippantly divorcing good husbands because they didn't "feel it" with them, and thus there is a large proportion of such women around. On the flip side, the Chads who had knocked them up move on to younger, childless women, thus removing women from that part of the dating market - and there are even Chad-mates in waiting as some single women hold out to try and bag a Chad
As someone who had attempted, because of the total lack of decent single women around (mid '90s), to date single mommies (but always bailed out after the 1st date because of the total embarrassment I felt about becoming a stepfather
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),