I think it's the fashion trend. Fashion trend is a life style which is popular in a group of people at a period of time. It's a social phenomenon in which a certain number of people imitate each other at a certain historical period. So if a lot of people wear this black nerd glasses, especially some fashion superstar follow this, I think it will be a trend.
Black nerd glasses still reign the fashion world. No doubt about that. Just check out those megastars who adore them: Justin Timberlake, Justin Bieber, Anne Hathaway, Johnny Depp, and so on. They are all ardent lover of black nerd glasses. In my opinion, as long as these glasses make you look cute and adorable, these spectacles are great. No need to bother about what others say about it. If you are uncertain about what to wear, bear in mind that to follow celebrities is never gonna go amiss.