Century homes with nowhere to put ductwork
Large parts of the city went up before forced air was standard. Heritage Hill, East Hills, Eastown, and the West Side are full of homes originally heated by gravity furnaces or boilers, with plaster walls, balloon framing, and no chase to run a trunk line through. Retrofitting these is a design problem before it is an installation problem. Sometimes the honest answer is a ductless or high-velocity system rather than forcing conventional ductwork into a house that was never built for it.
Boilers that do not need replacing
A working boiler is not automatically something to rip out. Plenty of Grand Rapids homes are heated well by original hydronic systems that need service, a circulator, or a modern control rather than a conversion. Where the homeowner also wants air conditioning, adding a ductless system alongside the boiler is usually cheaper and far less destructive than tearing the house apart for ducts.
Second floors that will not cool
The most common comfort complaint in the older neighborhoods is not a broken furnace. It is an upstairs that stays hot all summer. Usually the supply side was extended during a remodel and the return side never was, so the system cannot move the air it is producing. That is a load and duct problem, not a reason to buy a bigger condenser.
Weather and geography
Grand Rapids sits in the lake-effect snow belt, so a furnace here runs long cycles through stretches of genuinely cold weather. Summers are humid enough that cooling is as much about moisture removal as temperature. Equipment sized only for the peak temperature tends to short cycle and leave a house cold and clammy at the same time.