People don't forget to do that stuff. Drywaller shows up with crew. Insulation is not in. A lot of people just shrug and install the drywall. Maybe they are in a good mood and have another job close by that they can go to after informing the GC about the insulation. My money is on them just throwing up the drywall. Imagine the "bastard operator from hell" and you will have a good feel for how they view you and your house...typically. There are some craftsman out there but good luck finding them.