You can't just extend a house willy nilly. You have to set up scaffolding, destroy some walls, have temporary rigs to keep the ceilings from collapsing, etc. Unless you want to live in a "shipping container" building, but even then there's a non 0 effort, and the shipping container constraint comes with its own set of issues.

In real life, you just can't have it both ways. There's always a trade off. If the trade makes sense go for it I say, but I think people aren't always honest (to me or themselves) about the exact trade they are making.