Estate sales are commonly held by the estates of the recently deceased. So, there may be some bias in your sampling, since you're walking around the house of someone who was at the end of their life, not right in the heart of it.
And, I'm not sure large houses are as wasteful as you let on. After all, the floor area of a room grows quicker than the perimeter does. A 100 sq ft room could have 40' of walls, but a room with 4x the area could only have 2x the length of walls.
And it might just be my area, but there is no way you can get a bespoke home of equivalent square footage as you could a pre-built mcmansion.
In this area, people will do estate sales when they move as well. These are very much alive families, maybe their kids have mostly moved out. Totally not dead people homes. Those are a lot smaller and quaint.
And, I'm not sure large houses are as wasteful as you let on. After all, the floor area of a room grows quicker than the perimeter does. A 100 sq ft room could have 40' of walls, but a room with 4x the area could only have 2x the length of walls.
And it might just be my area, but there is no way you can get a bespoke home of equivalent square footage as you could a pre-built mcmansion.