Well, it probably stems from the issue that when you are "special" (as in popular), there will be a vast amount of 2 kinds of people:

• the common people infatuated with your public image, which automatically creates an emotional distance for the popular one. Even if this distance can be overcome, there is still the issue of a massive power imbalance in any relationship of that kind.
• the common people who want to use your popularity for their own means; those people will also be very adept at lying to your face.

So it's no wonder that popular figures tend to have relationships with other popular figures. They move in the same circles (and as we know, it needs opportunity to land in a relationship at all), and their lived experiences are more similar than those of less public figures.