never sell and borrow against BTC

Ive been reading that one strategy with BTC is to never sell and instead borrow agains it.
I understand that some of the benefits include avoid capital gains taxes ( we are not selling an asset), but also you can get to keep the asset. Additional advantages might kick in if the fiat we receive then is losing value and then the fiat we have to pay would have less value than the fiat we got at the beginning of the loan.

My question however is: why would someone lend money instead of buying BTC with it?. in a hyperbitcoinized world why would someone lend fiat to get fiat back, instead of buying BTC with it?