The government raises too much tax revenue from housing (eg....

The government raises too much tax revenue from housing (eg. stamp duty, GST, land tax etc) therefore they won't allow the price of houses to drop as their income stream depends on it. If it looks like it will fall they'll just open up the market to foreign ownership, like they did last time. They don't really care whether or not you can afford your house. Investors will reap the benefit, especially if they have bought in capital cities, and everyone else will be locked out.