'Used to' doesn't necessarily mean you have to enjoy or prefer it, though.

Ah, that depends on the kind of expansion, and how the original was built in the first place. Adding extra rooms on ground level would simply be a matter of building a structure abutting the original and knocking a hole in the wall between them. But adding additional levels on top, or increasing the height or size of existing rooms, can run into various issues. For example, you cannot remove certain load-bearing parts of a wall, and if you want to build upward you'd have to make sure that your existing structure can support what you have planned as well as essentially rebuilding the roof.

Adding a basement level underneath after the fact would be particularly difficult, or anything else that would modify the foundations.