They still had installment plans for buying appliances and repossessions. I'm pretty sure usurious loans have existed since money was invented.

Of course. Loans have existed since the beginning of money. That doesn't mean average people were using credit and loans to buy everything from Lambos to Cheetos to pornos like they can today. Not until very recently. Credit wasn't really something that was available to most people until around the 70s when it began to be digitized successfully. The psychology of debt today compared to that of a few generations ago is entirely different.

If you know the general store owner or your pub landlord and you ask them to put something on your tab, that's credit. Exact payment on the spot is what develops when you're trading with strangers.

Haven't (later) Millennials already learned from the mistakes of those before them? I know I'm scared of any type of debt due to the stories I've heard about it going wrong.

Yep, various holy books talk about usury and they're quite old.

It’s not so much about stinginess as unwillingness to seek medical attention because it’s so highly correlated with unbearable medical debt.