I'd call this a natural consequence of the changing dynamics of expectation. Being on the cover changes the way people see themselves, and they have to metabolize a different set of conditions. They're supposed to be superstars now, and if they don't live up to that, they've somehow failed. This changing perception causes many athletes to feel pressure and have a much harder time achieving their ideal performance. The Jinx isn't just a cover phenomenon. It occurs whenever an athlete receives a particular level of attention that builds expectation.