Fashion and Trends

So fashion and Trends absolutely baffle me. How does such a large group of people collectively decide that that style or thing is "cool" and they like it. And how is this information so easily agreed on and spread.

Ok so not unusual for an autistic person to not have any interest in following fashion and Trends etc. But it blows my mind how easily they happen. How can something be totally in now that 10 years ago would have been an absolute no. How does everyone know this information? And why do they all agree without question? Yes the internet plays a part these days but fashion etc was around long before the internet.

The 6/7 trend in schools particularly baffled me. One guy says it on the internet and now all the school children in the country and in other countries think it's the funniest thing ever. How do people that have never met agree that something is so funny it should be regularly repeated? It really was never very funny to begin with.

Again you might say well it's the internet and social media. When I was a kid and the internet was not widely used yet, particularly by kids and social media was not yet a thing. It was those alien egg things in the slimy stuff. They were the thing to have. Who knows why because they didn't actually do anything. But kids everywhere wanted them. How do kids that have never met, live in completely different areas, all go berserk over the same naff toy at the same time? I just don't get it.