You must remember that YIP
was built during WW II
as the airport for Ford's B-24 bomber plant. At that time the airlines were using Detroit City Airport (DET)
and serving it with DC-3s. DET was too small to handle the upcoming four engined airliners and because it was right in the middle of a residental area ir could not be expanded.
After the war one of the hangars at YIP
was converted into a terminal building.
The conversion mainly consisted of adding ticket counters and the other things that go inside a terminal. Two boarding fingers were added. As I recall they were made of wood. They also added an observation deck. The original large hangar doors were left in place. When the airlines moved to DTW
the terminal was turned back to a hangar.
As was mentioned the place is right out of the 1950's. The only passenger flights that go into YIP
are sports teams playing U of M. When they arrive the passengers get right onto busses.
In order to have any passenger operations out of YIP
they would have to build a new terminal, update the roads and a whole lot of other things. The cost of doing that would be prohibative.