This WaPo article and specifically the chart entitled "Young men driving the decline in sex": https://www.washingtonpost.com/business/2019/03/29/share-ame...

I read the chart as indicating a jump from ~15% to 28% of men 18-30 not having sex, and women from ~13% to 18%. So perhaps the simultaneous rise could be due to factors like less promiscuity overall or more selectivity, but I find that GP's reasoning is plausible for explaining why sexlessness in men rose higher and faster than that in women.