The reason it is so high is that it was set a long time ago on a sliding scale, and bracket creep of house prices means that every house traded is on the old 'high' value.
As a result, housing liquidity is low and people sit on unsuitable houses for long periods of time because they can't afford to sell and buy another. This leads to excessive commuting as people drive long distances rather than move closer to jobs, and leads to old people staying in oversized houses, tying up housing stock.
With a median priced home, if you sell it, and buy another of identical value, you will have spent nearly $50,000 on agents fees, stamp duties and other costs.
I would dearly love someone to explain to me how that is a good idea, fair or any other justification.