Are jeans American uniform?

Recently I went to two big events around Seattle and recognized that many people worn jeans.
One event was North West women’s show. As the name indicates, the attendants were mostly women. It was held at QWEST field. As you see in the picture on the left, the more than a half of the women in the picture wore jeans. Another event was Hops & Props at the museum of flight. This was the beer tasting event. More men attended to this event than women. While I was waiting to entering door in the long line, I observed the people in the line and saw so many legs with jeans. I didn’t realize so many people wear jeans. Then I remembered when my father visited me from Japan, he mentioned that everyone wears jeans. He used to wear his trousers until he realized that he look different from others with his gray pants. He started wearing his only blue jeans which he hardly worn in his house in Japan. He wore his jeans every day until the day he left Seattle.
I used to wear Blue jeans often. Recently I seldom wear my jeans because I like to look better by wearing other pants when I go out.

By the way, my sons don't wear jeans. They wear sweat pants instead.