The explanation GP provided is extremely low cost of entry. An agent doesn't even need an office. Here is my country many agents go free wheeling with a phone number and a bike. All they need is some connections with homeowners and they're off to business.
The natural end condition of an unregulated market is a monopoly. That is why we need regulation.
So, something is operating to provide implicit regulation. In this case it seems like chaos serves that role. Monopoly relies on a self-ordering property common to most market conditions.