Faulty ignition switches, overheating exhaust systems, seat belts and air bags that don't work as they should, electric steering boxes going bad, etc... just a few of the current problems covered by GM recalls this year.
If bad engineering and bad design aren't the cause, then what is? Cost-cutting probably plays a part, of course... but it would seem to me that poor engineering and/or design has to be a part of at least some of these recalls. It can't all just be el cheapo parts.