It's just a reinforcement loop where the more of something you have the more it accelerates. It happens in many places: bank runs (as soon as people start taking money out, more start doing so), the dead sea effect (where the best people leave and people start leaving as the median quality of coworker drops), hiring (where the more capable you are the more likely you are to get hired, so it gets harder and harder to hire the later you are to the game - most obvious with when you're interviewing interns or whatever), and so on.