lending/borrowing bitcoin doesnt have any sense, lending/borrowing is something that you do with hard-divisible non-fungible assets (like your home or your car) to have liquidity and preserve the ownership of your asset paying a fee on that across time.

Lend bitcoin to a custodial is selling bitcoin + paying a fees.

Some cases scenario in the lending timeframe:

1) Bitcoin prices stay pretty the same.

In this case you will end preferring buy bitcoin at market price then pay the loan for market price + loan fees. You are loosing money on that operation.

2) bitcoin price goes down.

you clearly better buy new bitcoin at the lower market price then repay the loans at higher market price + loan fees. You are loosing money on that operation.

3) bitcoin price goes up and up...

Cool, this is the scenario where this operation is profitable for you. Now, you know its good to have bitcoin cause the price goes ever up. Then why the fuck you expect some actor in the market would gift you free momey by accepting a so retarded deal? How is this sustainable for their business?

I'm a "go bitcoin-only, spend bitcoin and just sell bitcoin when you need to spend in fiat" maxi and think that "lending bitcoin" is a retarded psyop.

Lending bitcoin is, at best, an high-risk trading move, not the "best way to spend bitcoin" they are selling.