"would you lend me all your bitcoin for 5 years without any interest?"

In such a scenario, interest would not be the deciding factor for me.

"why would you like to have a credit if you cannot pay it back?"

Not all with good intentions are well suited to predict future happenings.
In some cases there is intent to defaud.

"I will not ask for a credit at 30% interest yearly for sure, but I will for a 3%"

Let us not forget, 3% or 30%, usury has much negative potential, including violence.