Well its a pyramid scheme like many of the state licensed businesses. The low level agents have to work for a broker who soaks up the majority of the commission. Only after being an indentured slave for a few years do they get the "privilege" of themselves becoming a broker. The problem is that once that happens no one will hire you, so your on your own for finding clients/advertising/etc. That takes capital most low level agents haven't managed to accumulate working for someone else. So its likely they need a significant other/whatever to support them while they build the business while competing with the larger agencies that have the money to plaster signs down the freeway and run advertisements.

Given some luck/skill and a lot of hard work, maybe they become large enough to start hiring agents themselves, and the cycle repeats.