Supply and Demand, pure and simple. Try finding a 1 or 2 bedroom apartment in West Bay, even a decent 3 bedroom is not easy to find! Prices are actually going up!! Even the Pearl isn't that easy, with friends of mine struggling to find a decent 2 bedroom furnished apartment. You can find, but not in the decent towers away from the main construction.
As with anywhere in the world, if you want to stay in the premium places you're going to spend more money....granted, you could live in some amazing places in other cities, but you'd also have A LOT more choice of locations and properties.
It's a knock on effect down the market. No signs of this changing.