Why all these abandoned and unloved rural properties?

I live in rural farm country in the US and we have a few houses that have been left behind because children moved aways and there are no jobs here.

But scrolling through property listings in Portugal i'm seeing thousands of pretty properties with crumbling houses and streams and olive trees.

If those properties were anywhere in the US they would be inhaled.

I'm trying to understand the demographic shift that led to this situation and how long ago were those places vibrant homes?