I don't argue with your basic premise (companies pay the cheapest contractor, etc), but it is worth noting that because of those pressures, many experienced people leave the industry, thus creating the lack of workers they are talking about. Reversing that change is slow, even if wages rise, and there is no instant fix. Getting people who have left for another industry to return can be difficult, especially in the case of people selling off tools, etc. where the cost to re-enter is often too high to justify.

Add on to that, developers have no incentive to construct everything at once, thus stalling future growth for their company and over saturating the market, driving down housing prices and their enormous margins.