You'd need to have people like gardeners, maintenence staff, and cleaners just to stop nature taking over. To actually fix problems you need conservators and specialist builders. Plus you have to heat the place to prevent damp and mould.
My family inherited a large estate in the South of France and the roof alone was half a million. Now you don’t have to fix things right away, but it quickly becomes a hazard.
When they where fixing the roof of Notre-dame, they had to source wood (oak) that was as old as the original. That kind of thing would really accelerate costs.
