No, I'm not picturing any force. Keep in mind that "communities" are not just geographic entities. They're a network of personal relationships.
If, say, someone from a poor black neighborhood makes it big with the help of Affirmative Action, he may wind up moving to a rich neighborhood, but he'll still maintain many of his personal relationships, as well as an emotional connection to the old neighborhood. That will mean, for example, that a bunch of poor black people in the neighborhood have an uncle, cousin, former classmate, coworker, or teammate, who is now a successful businessman. That will create a valuable role-model or even a mentor, as well as connections that could help other ambitious people in the neighborhood move up in the world, even if he no longer lives next door. And, as in the case of Lebron James's school, the successful people can wind up pouring resources back into the area, even if they live outside of it, and acting as a voice for the neighborhood with powerful people who might otherwise never hear the message.
This kind of thing can expand horizons. If you live somewhere that the only people you've ever heard getting rich did it by being drug dealers or basketball players, the chances of you making wise decisions is pretty small. But if you also know of a number of people who started in the neighborhood and then "moved on up" based on studying hard, working long hours, and staying out of trouble with the law, your chances of making wise decisions is going to go way up.