The way the market seems to compensate for this is that more agents flood into that job market for a given number of houses, and then they spend proportionally more time trying to find clients. They spend a relatively small fraction of their time actually helping existing clients in very hot markets, since they just don't have many (except the few top agents/brokers, who do very well for themselves).

But spending all your time finding clients isn't actually useful work in helping transactions happen, so it's less and less efficient as the home values go up.

At least that's what I've observed from a distance.