But actually, it's because people have a limit on how many other people they can keep track of. Robin Dunbar, of Dunbar's number fame, suggested the limits were

But actually, it's because people have a limit on how many other people they can keep track of. Robin Dunbar, of Dunbar's number fame, suggested the limits were around 500 people as acquaintances and around 1,500 people whom you could recognize. Beyond that, other people may as well not exist. When communication at a distance was hard and the world was more insular, the faces you'd recognize would be mostly of people in your community. Still, even within a community, you were going to take more interest in the local movers and shakers over the hobo on the street. Our modern, interconnected global village just scales that up. We still focus on the movers and shakers and ignore the hobos just the same. But now, instead of everyone in a community recognizing the same 600 locals, everyone in the world now recognizes the same 600 people. Which is also how they become so rich. Need to buy a widget? You're not going to seek out a hobo to see if he has any in his beat up old shopping cart, are you? (well most won't, anyway) You're going to go to straight to the guy you already know. When communities were insular that meant some small number of people in the community were richer than the rest, but there was a pretty hard limit on how rich they could become when there were only so many local buyers. The difference now is, again, a matter of scale. When the entire world wants to buy from the same person, that hard limit becomes multiplied by a very large multiplier.