Another aspect auto design incorporates is design for manufacture. Mold injected plastic parts are cheap even though they snap together and apart poorly sometimes making tasks like getting up inside paneling to get at harnesses, light bulbs, or mechanical linkages a pure pain in the ass.
The bottom line is a lot like henry06x is talking about. They marketing and product platform development big wigs set a consumer price per unit and a list of performance requirements at the 10,000 ft level. If they have to use a few cheap parts or funky designs that suck to take apart in order to design a car than be built in a cheaper, more labor-friendly manor then the auto shop mechanics and DIY types are going to get the screw and that's about all there is to it. Even if they come up with a better design before going into manufacturing, they may not implement it because of the cost and time to retool or retrain workers. Even "premium" brands are subject to this since they still have to design for manufacture because they do build cars in large enough volumes.
Some things really seem like oversight, though. Especially interior plasticky stuff. At least mechanical parts are rigid and designed to tolerance and pretty much go back together.