People are Sheep for the most part. They follow the herd. Whatever looks like it's becoming trendy, they jump aboard. Same thing happened in the 90's with Sideburns, when that Beverly Hills 90210 show came out, wih the main characters sporting sideburns. Almost instantaneously, every dude started growing side burns just like the characters on TV.
It was viral pic of a beard on a French Rugby star about two years ago that started the Beard bandwagon rolling.