If you have a car, why would you take out a car loan? If you have a house, why would you take out a mortgage? If you have a rental property, why would you take out a mortgage against your rental property?

Probably the most analogous to most loans taken out on this forum, if you have a stock portfolio, why would you take out a margin loan?

Answer the above questions, and you will understand why someone with collateral might take out a loan.