But with bitcoin you can't loan money that doesn't exist.
Bitcoin will never replace FIAT. They'll coexist. If bitcoin will be deemed as the only currency that we can use then lending is possible. People will always try to find ways to lend out money. How can we use bitcoin as a mode of payment if it doesn't exist?
For now,bitcoin is not yet accepted as a mode of payment so it cannot be used in all money transactions.We should still make use of fiat while bitcoins are not yet available to use.But hopefully in the next years,bitcoin will be develop in the market too.