So the ratio of median home prices to median family income has moved from about 3 to about 4.5 over the last 50 years.

This is because the many manufactured things have dropped in price over that period of time. This has meant that families have more money available to spend on things that are not manufactured. Land is the epitome of something that cannot be manufactured, so goes up in value.

Here's an article on Baumol's cost disease which explains this: https://www.vox.com/new-money/2017/5/4/15547364/baumol-cost-...