Modern design often requires larger rooms than houses had in the past, so opening the walls is usually part of a renovation. They might look a bit worn before the renovation, but drywall could be only the first layer uncovered. This is a relatively modern material, so it could be covering up an interesting collection of materials that were used to cover the aged walls that originally graced the structure.
Lath and plaster were very popular for many years, but they would not necessarily have been original to the structure. Some houses had brick walls inside and out, but other building materials were stone, large pieces of wood laid vertically, and even smaller wood pieces that may have been covered in paper that has rotted and disappeared with age.
It could seem like a nightmare to continue finding yet more walls underneath the present ones, yet many original walls are in good shape. They may need a bit of sanding or repair, and some of them could need only a new paint job to be beautiful. Opening up one wall could become an archaeological experience for those willing to undertake the challenge.