It's also short-sighted; present-thinking to a fault (unfortunately, all-too-common). As an example: many of the Gilded Age mansions that helped revitalize Newport, RI tourism (and, essentially, the local economy as a whole, after the Navy mostly left) were basically abandoned for many years. Nobody cared about preserving the decadent detritus of robber barons (because, as you said, people were more concerned with common economic troubles). Attitudes change and lines go up; the jazz fest brought deep pockets and people remembered you could summer somewhere other than the Hamptons. On the other side of the coin, before Enes Yilmazer and after LOTRAF, they served as a publicly-accessible view into filthy rich-itude. Maybe we head towards another depression at some point, and people decide preserving these iconic relics isn't worth it anymore. But that's not an absolute state, just a product of shifting dynamics which we can't really scope out fully without some distance.

How does legally requiring people to leave up unused "historial" buildings prevent foreign investment, strip malls, or parking lots? These seem like completely different issues to me.

Those things are 'mittel zum zweck' German saying for it's just a necessary medium for the intended purpose.

You don't go to the Cinema because of the building, you go for the movie, friends,. atmosphere etc

Sure. Let the squatters have it if it's worthless it doesn't matter. And while you're at it ban foreign ownership on property.