Absolute nonsense. Why would a "speculator" refuse to rent out their property and make a profit out of it?
Sometimes seemingly abandoned buildings are used for one-off occasions which generate income: downtown LA is full of "historic" buildings which the owners allow to dilapidate outside of a few areas they can rent out once or twice a year to a film crew.
edit: another thing -- rich people procrastinate too, in fact many of them can afford to procrastinate on matters like this, and they may rather take a loss than confront the anxiety and work of selling or renting out the property
Just for reference, in a small city (40K people, 8 sq. km.) you can find 2K empty properties out of the market because it's more profitable to wait prices to raise.