I notice that the high end interior painters I use always insist on either using a roller or a brush. They never want to use a spray gun.
I know cars are painted with a spray gun, so I really don't understand why they think a spray gun will produce a bad quality finish.
Best Answer
It isn't the quality of the paint, though the different processing (cars: paint then bake it on, buildings: paint, let air dry for days) may be part of it.
It has to do with preparation and control.
A new car is NOT spray-painted after full assembly. To do that, you would have to mask the tires, windshield, windows, chrome, etc. Literally the entire metal shell of the car and nothing else is spray-painted. There is no harm (except wasted paint) by spraying where you shouldn't.
A house, even new, is not setup for spray-painting. You have electrical (though if you see paint inside junction boxes, that could explain it), plumbing, windows, etc. all of which are installed (to varying degrees) before the main paint job. Plus houses are routinely painted years later as a house may last 50 years or more - few cars last anywhere near that long.
Even over a relatively long car lifetime - e.g., 20 years - the original paint job will generally need only touch-ups as it is typically quite rugged, with multiple layers designed to hold up against years of use, UV radiation, weather, etc.
When repainting a car, typically after accident damage, spray-painting is used. The extra effort involved is significant, but brush marks on metal car body are a bit more of a problem than on house walls and it is the only practical way to match the original finish. But it is an ordeal - and most people never repaint their car unless it is seriously damaged.