A full appliance package can be bought for under 2 grand retail. You can save a little bit of labor/material by eliminating the need for a couple circuits, but not that much. Not much extra work to pull additional wires if you already have to do one. So the savings just aren't there to meaningfully impact the housing cost.

You're talking out of both sides of your mouth here. You say that kitchens and bathrooms are the "big cost items" yet here you say that omitting or scaling them back doesn't save much. How can both things be true?

Appliances are cheap-ish. The structure and space for extra bathrooms or a full kitchen are much more expensive than a full appliance package.

So you can save money - but not much - by not having full appliances. You can save a lot more by not building a full kitchen and a second bathroom.