Companies like Amazon literally own billions in office space. Making that space valuable again with RTO policies, especially if you create an RTO trend, a way of enabling them to sell at their previous values.
Or, as we have seen hundreds of times, it's sold at market price to a "third party" company that is actually owned by one of the board members or executives, which then rent it back to the company for a slight premium.
But this isn't the norm, and it's not happening to well-managed businesses. It's something a vulture does after the company has been struggling for years. If that happened with a Microsoft or an Amazon, or any of the companies we work for. It's silly to suggest that is the cause of widespread RTO mandates.