[jjav]

> If you wanted to make that much money from rent

It's not either/or, which is why I'd assume the parent poster called it weird. That investor could make the appreciation and of top of it could make the rental income. So it is weird, from their perspective, to leave it empty. If they're flipping real estate for profit (as opposed to buying a home to live) why reject the extra income.

Also, selling a rental property with a solid history of rental income tends to be better than one with a history of sitting empty. Although that probably doesn't apply to mansions.