When the frame is put up it is typically inspected to ensure it meets code and that correct fasteners and brackets are used. Until the inspection is done you don't see roofing and electrical finished up. Then you have the electrical and plumbing on top the foundation. And when that is in its inspected again. Also heating cooling piping. Then fiber insulation is put in walls, then you have your drywall installed. Then you have the different finish teams come in. Finish plumbing, cabinetry, tiling, floors. And then another round of builder inspection. Then you get to the city and bank inspections.

Any one of the inspections or the specilaty teams running slow can push the whole project back. If your AC ducts aren't in you can't drywall for example.