People can build houses with the same characteristics of the 1970s and would likely be able to afford them. But people want modern sizes with all the appliances and nice kitchens, two car garages and whatnot.
Sure. But that's due to low unit build + immigration creating demand combined with builders mainly building 2500 sq ft houses. Back in the 70s it would have been 1,500 sq ft. But also people want amenities like central air, game rooms, big kitchens, etc. It's like making sedans vs SUVs. MFGs make money on S/CUVs and larger houses. Small units don't have the same unit profit.