It seems you’re talking from the developer’s point of view, the person who writes and deploys smart contracts. I am coming from the end user’s point of view, who has very little to gain from the immutability guarantees.

For Uniswap pools, you’re referring to smart contracts that allow people to take out or provide funding for loans, right? So the immutability of the contract may be appealing in terms of interest rates or loan duration/terms/etc. But this option already exists outside of DeFi (fixed rate loans). It is cool that we can offer these in a decentralized manner, but the possibility of a bug affecting my mortgage or another sizable loan is a huge, huge deterrent and I am also sure that, if DeFi “takes off,” there will be solutions implemented that completely remove all immutability guarantees.

Immutability is the least of DeFi's problems. A DeFi "loan" requires that the borrower must put up an amount equal to the sum of all future installments... which means for a borrower to be able to borrow funds they need to already have the funds they're borrowing (plus interest).