Yes, it looks very good on paper: Keep your bitcoin and get fiat to buy a house for example. But...

- You lose complete ownership on your BTC. What prevents some companies with funny names ("YouHodler" - seriously! - ) and created only 2 years ago to escape with your BTC?
- the LTV (the amount of BTC you need to put as collateral) is usually 100% of the loan!
- AND you pay also interest rate on that: So the lender gets your bitcoins (that he can borrow to others) + the interest rate that you gave him!
- Not to mention that if the price of Bitcoin decreases, you have to increase the amount of BTC put as collateral.
Imagine taking a loan and each months the lender asks you your month salary and alters your loan if he detected that your salary has decreased!

Bitcoin-backed loans are really insane and they make no sense at all!
I guess that's because there are absolutely no competition on this market for the moment.