Earlier quoted context omitted.
This might still be appealing to young people, especially those who do not like the noise/pollution of big cities and can't afford them?
Do you have any idea of the thermal inertia of a castle? How are you going to heat it to an acceptable living temperature?
The real problems are that stone is a terrible insulator, that single-pane windows are even worse, and that air leakage in old structures is incredibly wasteful.