Neat chart, interesting. First, look at the Vietnam years 1965-74, pretty much nothing happening there. Jump up during Carter's presidency. Then the first four years of Reagan was the recession, so it dropped, second four years, the boom.
Then look at mortgage debt after the S&L crisis, from 1991 to 2000, no growth relative to GDP, but other consumer debt was rising. That was the time to buy a house.
Since 2000 - yeesh, what a mess.