It's pretty easily explained, they think it's cool to say they are nonbinary, or pansexual, or genderfluid, or something along those lines. One popular/alpha kid says it and soon their entire clique gloms on. Adding to the allure for teens is that some adults find this shocking. They are not really committing to anything, and they know it. They're doing it for social karma. Teens have done this kind of thing forever.