Foreigners would have the money to buy it and keep it up. Or British movie stars and rock stars. The woman who renovated Cassillis is Australian. Jeremy
Irons renovated a similar type castle in Ireland. There are many small Scottish tower houses/castles, many! They and Victoriana are my main interest in architecture.
Many years ago when I was 25 years old I went on a solo trip to the UK and one of my areas of interest was tracking down some of those Scottish tower houses. I’ve visited several, some in ruins, some all fixed up. One of the ruins was Stuart castle outside of Inverness. I took a few photos of it. It was wonderful when 25 years later DH and I were able to stay in that castle. It was by then a high end bed-and-breakfast. It was great to compare the Before and After photos. It had been purchased and renovated by someone with the last name of Stuart who is a Canadian businessman multimillionaire.