Houses depreciate. Markets can do funny things (remember the COVID days when a used car could sell for more than the same new car?), but generally the remaining value of a standing structure is going to be a fair bit less than the cost to build the same thing new. It is likely that the parent also sees >50% land value on the current property now that the house has been lived in and is showing some wear and tear, but key here is that to rebuild the building from scratch it would cost as much as the land plus current building is worth just to build the same structure again.