Why are a lot of people seem to have jeans/denim ?

Okay. I know this is a very common that people have. But I just know that by experience. I don't know exactly why but I mean, jeans/denim are just a normal clothing garment. Anyway, this is what happened to me. Since its summer time, I went to the beach, just a few days ago, to spend some time swimming and hanging out with my family on a hot weekend. Since we spend most of the time swimming with our surf boards and just frolicking in the waves, I was wearing a black bikini. But as soon as I got out of the water, I just put on my low-rise jeans and just left on my bikini top on, and was still wet. As I ped by a group of guys, they whistled at me and one of them even had the courage to tell me how y and hot I looked. So after this, I ask myself, "Why do a lot of people seemed to get by denim/jeans?" or why do you think they got excited to see me in just a bikini top and jeans? Just curious:) Need good answers cuz this has raised my intention to ask this question.