Licensing costs and restrictions. Barriers to entry put up by the rich plutocrats to keep the middle class in it's place.
Why do you think that should stop someone if everyone is subject to the same rules? I can operate under an LLC and build wealth at minimal cost.
Let's say a poor person wants to start a restaurant in a city in which he is currently residing. Let's say the competition serves alcohol. Let's say the cost for a license to serve alcohol is 250k. In order for someone to start a restaurant that serves booze, thus would need to start big enough to afford the cost of license, or they would have to compete without serving. Thus giving the larger "richer" competition a big advantage. Hell the rich restaurant could even under charge for food and over charge for booze to try to drive the poor guy out of business.
Same rules... but now the poor guy with no assets to put up has to look for rich investors who will own a part of his business or has to find small niches.
In many cities you can't even get licenses to do certain things, you have to already have one that was given out in the past.