I live in a building that's been sold three times so far. You are aware people sell real estate sometimes?

Obviously, but they are likely taking that money to invest in more profitable real-estate elsewhere. The ultimate goal here is to reduce the consolidation on the ownership of real-estate, meaning these investors will ultimately lose value. Morally, they could and should abdicate, but since when has that motivated the wealthy?

The mechanisms do exist for your suggestion, and some owners would actually be okay with it, but I would still expect a lot of opposition.

Look into the history of eminent domain too see (historically) just how receptive land owners have been to selling their land to the government.

All this is basically just to illustrate my original point:

Complex economies rarely have "super simple solutions" without pitfalls

I don't think that's a reason for inaction, but it does explain why real change is so hard to actually implement at scale.