No idea why you're being downvoted. This meme (rich people buying luxury condos, letting them sit vacant, and then profiting somehow) doesn't make any sense, and that article posted as evidence for it undermines it by depicting those units as being un-rentable due to oversupply in the market.
And in the meantime, they choose not to rent it why? The intuitive answer is: they're hard to rent, because there's way more luxury condos available to be rented than people who want to rent them, and it was a bad investment that the rich person will probably lose money on (if not in absolute dollars, then in comparison to some other property that is desirable to rent). But a lot of people in this thread seem to think it's intentional and rich people have some devious way of making more from a vacant condo than a rented one.