Curious. "Smart contracts", for the the layman, is really just "automation". Is there a real need to "decentralize" it, and make it unstoppable from human intervention?
I believe the DAO was an example that it shouldn't.
The way De-Fi is working on all of these platforms is that you stake or lock your tokens in their contracts on the ethereum blockchain. The contract then allows borrowers to take loans and pay interest on it. The value of the liquidity that lenders provide to contract is balanced automatically based on data obtained from exchanges. Traders who will jump at any arbitrage opportunities ensure that the "pegs" are maintained.
In a way, this does provide a kind of bank on the blockchain into which you can deposit money and from which you can borrow money. It is decentralized so you aren't actually trusting anybody except the robustness of the code itself. The problem is that even for a simple implementation, the transaction costs and time becomes too steep for any PoW chain (Like ETH in this case). If instead PoS is used, it becomes a whole new question of whether it is decentralized anymore. What really happens in practice is that any small player is driven out simply on the basis of transaction fees. It ends up as nothing but a place for price manipulation and arbitrage milking for whales and traders who are expert at this sort of thing.
To answer your question, yes, there is a need to decentralize. But, there isn't yet any way to do it without these other pitfalls which make the whole system pointless.