They are so interesting! I learned from the tour bus to F and M that it is illegal to remove them. They must be allowed to disintegrate, per the tour guide. As you've likely observed, people still build new ones on their property, often matching the exterior colors to the main house.
I was intrigued by these also and asked my hosts in Morgade about them. A young man there told me that people from as far away as New York and London now want them in their gardens and you can get good money for them.
I can't imagine how you would get a centuries old stone horreo to NYC, but I guess with enough $$ you can do anything.
Somewhere closer to Santiago I did see some miniature ones which looked more ornamental than useful.
It may have been near the photo attached... I'd reached peak Horreo photo by then so didn't take one of the miniatures