The electricians are actually pretty poor guys when it comes to the general contractor. They probably can’t make a living from the house wiring alone. It’s only the upsizing that makes it interesting for them, because the home builder is inevitably tied to them. That’s how the juicy markups come about. And since hardly anyone builds to standard these days, they also get by.
But not if, for example, you take out the electrical work and have it done by an electrician. We also only had the shell, meaning the finished plastered house with windows and doors plus heating and water (due to warranty) done by the builder, and we did most of the rest ourselves. We were also able to design the floor plan ourselves individually. That way, the house looks the way we wanted, the equipment is according to our wishes, and for what we had done by the builder, we saved about 20-25% compared to contracting separately or through an architect.