Haha I think the explanation is that most of the big dick guys aged 18-21 are still babies sexually. So as they discover (to their delight) that they are hung in comparison to the average man, they want to show it off to anyone and everyone. They’re still likely to be sort of self-centered and immature/not able to maintain relationships at that age. Fortunately for them, big dicks are so sought after that they’ll get no shortage of chance haha. So by the time they hit your age, a lot of the big dicks have figured it out and are happily in relationships.

I’d be really curious to see a study of average penis size in relation to when you start dating a partner. I’d bet the results would show that on average, the older you are when starting a relationship, the more likely a partner is to have a smaller penis.