I think it was less that people prefered to cook things on a spit over an open fire. Its that open hearths were the default/only option for a very long time. Enclosed stoves didn’t become a thing in western countries until the 19th century. Enclosed ovens were large. The sort of thing that were community property or businesses (like Mills). Or restricted to large wealthy estates. And they weren’t part of main home or kitchen.
They were also often built as needed from available materials.
Spits were in many ways the most practical way to roast things if you didn’t have access to an oven. Even then since they required live stock, servants or available children. It was sort of an upperclass thing. With baking or roasting otherwise taking place in clay vessels, dutch ovens, or when an available big oven had already been lit up for bread baking. Or just not taking place at all.
Before the development of the modern middle class. Peasants mostly subsisted on stews, porridge, community baked bread and beer.
