Probably better to say "expected to" rather than "supposed to". The problem is that income growth is not evenly distributed across the income curve, but instead increases up the curve. So the net effect is that fewer and fewer high income entities own a greater and greater proportion of the housing, and lower income levels are increasingly forced to rent, or---at the extreme lower levels--go without housing. As a matter of public policy, this is not what we want to happen, though I'd agree it is what we should expect given current policies.