It isn't, at all. The increase in prices is tied to increase in GDP, interest rates and disposable income. Unless you think investing is a Ponzi scheme.
The problem is that this isn't true. Since 1965, home prices have increased 7.6x faster than income.[0] This obviously cannot continue indefinitely (that'd lead to everyone spending >100% of their income on housing), so at some point the price increase will have to stop.
It isn't, at all. The increase in prices is tied to increase in GDP, interest rates and disposable income. Unless you think investing is a Ponzi scheme.