In order for it to decrease prices, the rate of building would have to outpace the rate of demand. If you build 100 houses, but 1000 people move there, you can

In order for it to decrease prices, the rate of building would have to outpace the rate of demand. If you build 100 houses, but 1000 people move there, you can say "Oh look building more houses didn't help, prices still went up". It's not that building more didn't help, it's that you didn't do it enough. The obvious answer is to do it more, not to ... stop building houses as if that is going to bring prices down.