Interesting article and some fascinating videos… would love to visit these places
If anyone is looking for a project… perhaps… 
Apart from the cost , can you imagine the battles you would have with Batiments de France?
That is probably why they are still ruins.
It was a tongue in cheek question… Jane…
Most of these ruins are part of France’s heritage… 
some are being “saved”… some are not… did you watch the first video… they’ve been working on the first ruin for donkeys years…