I think that the core of hipsterdom is a desire to appropriate culture and self-identity with money. Buy a track bike, you can feel like you're a romanticized messenger: you don't care what people think of you, have no fear, and don't care about money (ironic isn't it?). Get the right fake retro 80s tee and you're suddenly obscure and irreverent. Carefully select really ugly glasses, and you can feel like you don't care what people think of you. Eat trendy foreign foods and you're cultured.
At this point it's so common a lot of people are acting this way just to fit in. The trouble is they tell themselves they're doing it NOT to fit in. It's excellent marketing. As soon as enough people buy the fad, you can market a new one and everyone has to buy new existential gear.

Disclaimer: I know lots of people have plenty of good reasons to ride track bikes or fond memories of the 80s. In fact, I've done every single thing I listed. I understand these motivations: it is very difficult to define oneself in an age when conformity is not acceptable. Human population (like any other data set) is by nature mostly average.