As Touboul described it:
Indeed, a random imbalance will be detected after some time and all anticonformist individuals will tend to disalign to this trend, regardless of the fact that an increasing proportion of them do and therefore yield a clear bias towards the opposite trend. This will be detected at later times, leading to a reciprocal switch, and these oscillations will periodically repeat. Despite their efforts, at all times, anticonformists fail being disaligned with the majority.
Translation: The hipsters are still recoiling from the mainstream, but each holds an outdated concept of what the mainstream is. Because they are slow to react, they end up all looking alike, and all changing fashions at the same time. (Irony of ironies!)