If BTC is such a pristine asset, how come I can't find anyone that gives a loan against BTC for less than 10 percent interest?

Even if I over-collateralize 2x, the interest rate is still way higher than mortgage.

I get that the opportunity cost for the lender is owning BTC themselves, and BTC tends to go up 50% per year.

But people are buying way more complicated instruments that yield 3-7%

Why isn't that capital being used for BTC backed loans instead?