My guess is that these large developments are more profitable, and likely a safer bet for the lender[[s).

It's probably like the "buy in bulk" theory. The more you buy, the less it costs.

In Chicago, smaller apartment/condo buildings are going up all the time. But, each unit can sell for a lot more than they can here. Therefore, if one unit sells in this hypothetical Chicago condo building, it will cover more of the cost of the development than the same size building in Detroit.

So, Detroit must build/sell lots of these units to cover the cost of the development.

If that makes any sense...