Because the value of a desired thing decreases/increases in proportion to its rarity - a privileged guy who attracts hot young women cannot fully grasp how privileged he is and focuses on other aspects such as utilizing his privilege to have sex with as many different women as possible without self-limiting himself by unintended impregnation or searching for qualities in women other than their looks non-privileged guys find banal or unremarkable.
Because young non-privileged guys who happen to have the highest chance to get access to the hot young girls in their prime (virgins) out of all non-privileged guys are too naive and inexperienced to fully appreciate the bond with a girl they established, never letting such a relationship progress past the conception phase, which they may regret years later.
Because they're smart and realize that if they manage to impregnate a hot young girl somehow, the chances of experiencing more harm than good in the long term are too high to be considered "cost-effective". Lousy upbringing, family terror and infidelity become quite possible scenarios.
While the opposite situation of impregnating a relatively unattractive woman opens a possibility for a loving, dedicated and attentive wife/mother, the absence of sexual attraction will "bubble up" elsewhere, potentially hampering the successful family model in unexpected ways.