Think of it as going to the pawnshop. You have some assets that you don't want to sell but you need money for a short period of time. You can guarantee with those assets that you will return the money to the lender and you will get your assets back.

If you don't want your assets back than you can just sell it and you have no need for a loan. This is exactly the reason that users who try to sell their collateral and also try to "borrow" money guaranteeing with the same collateral are given negative feedback.