Another point I think is worth mentioning, upon observation of the same girls who are right out of high school and seminary, and then again 5 years later, if they’re still single, very often their Tznius has deteriorated greatly.
Bec. of hardship in finding Shidduchim, their single status causes them great unhappiness and dissatisfaction and often a downturn in their level of Bitachon, combined with being unmarried and in the secular world, causing a decline in their Tznius.