>The whole point of a loan is that you're willing to pay extra over time in order to have access to more funds at the present

No, that's not the point of these loans at all. They are the equivalent of remortgaging your home to get cash. If need money for renovation and you have a lot of equity in your house you can borrow against it. They are doing the same thing with crypto. They don't want to sell their crypto because they want to speculate on it and they need money so they use it as collateral.

I personably think it's a very stupid idea to invest in something like crypto on credit. Lending your crypto to these morons looks like a pretty good idea if you can trust that the smart contracts doesn't have bugs. You get a stable and guaranteed >5% without all the risks of the stock market.