Centralization

When you trace all the way through, most DeFi protocols bottom out in a centralized oracle-often in the most crucial step.
Sometimes, this is a liquidation price oracle pointing to centralized exchange APIs. Other times it’s a council of token holders. Sometimes it’s the team of the protocol itself.
There’s a further problem too - most decentralizing protocols are computationally intensive. Fitting them into the ETH blockchain in a way that is cost-efficient and fast has mostly eluded the space.
That’s not to say that centralization is always bad! USDT, USDC, and similar tokens are great projects which have revolutionized the entire crypto industry. They power much of the volume, and if you want something that can be turned into a dollar 24/7 that’s the only game in town and probably always will be. Because fundamentally dollar bills aren’t on the blockchain, they’re in bank accounts.
But if what you want is pure DeFi, the options are few and far between.