> What serious borrower needs to pay 10% to access credit?

People who can make more than 10% trading?

Lending protocols aren't doing anything different than what banks do: allocating inactive capital to those who can make use of that capital and are willing to pay for it.

Interest rates are high because of A: market volatility, professional traders can easily make more than 10%, and B: information asymmetry, large capital pools haven't allocated to these pools.