Well, I for one prefer to live in cities, and I like to work in things like research and consulting. This is unfeasible from a rural area. Not everyone wants to run a B&B.
What is stopping people from occupying those places? Nothing, They are just not that attractive. Maybe the landscape is beautiful, but there are no jobs, no services, no social life, no culture/arts/entertainment... This is why their price went to zero. And still, there are few takers.
The Milan story is very different. Those are valuable spaces. People do not use them because they do not have the legal right to do so – they belong to the city. I predict there will be a lot of takers. If Edgeryders were in Italy, we'd definitely apply.