It’s not the only reason. There is no one reason.

Off the top of my head:

• Pension changes driving some boomers to nest egg in property which dove up prices
• Active destruction of public housing pushing more and more people into the public sector which drove up prices
• Tax incentives encouraging property speculation which drove up prices
• Allowance of foreign purchase which encouraged landbanking and laundering and pushed up prices
• New builds failing to keep pace with increase in population limiting availability and pushing up prices
• Volume builders land squatting and releasing less than required to maintain artificial scarcity and push up prices
• Failure to decentralise employment hubs coupled with failure to increase density pushing more people into the same area, causing scarcity and diving up prices