Renting them out is not selling, it's an ongoing income source for the owner. The renter does not determine the price when the alternative is to move elsewhere or live out of your car. There's simply not enough housing--supply is limited. It's not a simple equation like a factory adjusting the output and price of its widgets. If things were as simple as you say, there wouldn't be such a severe housing crisis in the US. Just search for US housing crisis, there are thousands of articles explaining what's going on.