DEFI lending platforms like Aave are decentralised finance protocols which enable anyone to either lend their crypto-assets (usually ethereum) for high % interest, or lock up their crypto-assets to borrow a fractional amount (usually up to 75%) of another crypto-asset.
For example, using Aave you could lock up $100 of Ethereum and get a loan of $75 in USDC.
There is an incentive to lend your cryptocurrency on a DEFI platform, because the platforms typically offer higher interest than a bank deposit. As a crypto-asset lender, you can get up to 9% PA on some assets, which is better than any bank deposit.
However, I don't see why anyone would borrow another crypto-asset using a DEFI website/protocol, because you need to lock up more collateral than the total loan is actually worth.
If the person already has enough crypto to trade into the other asset in the first place, then why would they bother borrowing it from a DEFI platform?