Technically, because they are just spawns like anything else, but it's possible that maps where objects like cars in Kings Row have dedicated spots so that the object spawns make sense. Just guessing, but the locations where you see mobs attacking a car on the side of the street have been coded on to the map to possible spawn like that or a regular spawn without object. Adding objects to Winter Lord spawns means that wherever the winter lord spawns an object will show up there that might not make sense. Consider just the locations in Atlas Park where you've got presents in the street, on the sidewalk, on rooftops, and so on. You would probably have to code individually for each spawn location to have an object show up that would make sense, such as some sort of rooftop appropriate object for rooftops, a car for the streets, etc. Might be easier to have Winter Lords spawn with non-combat civilian NPCs (like mobs that spawn with PPD officers to have shootouts) and they only run around in terror as they're being attacked because you could explain random civilians running in terror almost anywhere.