New electrical companies in my area get inspected pretty heavily. But once the company gets a reputation for doing solid work (typically by passing a handful of inspections), then the inspectors tend not to "waste the time" inspecting them so heavily. After all, they "know they do good work." SO, with the heat off, the electrical company starts cutting corners because they know the inspector isn't going to take the time to look at everything in detail. Add to that complaceny the fact that most homeowners have absolutely no clue about anything electrical, and the fact that the inspectors often let a lot of things slide, and you have the recipe for work that does not comply with the NEC. It really comes down to the contractor policing his own work.
Kevin