It's actually higher prime interest rates.
Sure, people can borrow at 3% interest (or whatever is provided) but why would banks want to necessarily want to loan out at such a low interest rate?
I don't understand the question. Are you asking why would banks use negative rates?
Pretty much. What's in it for the banks to loan out at incredibly low rates? Remember that there isn't only an aversion to high interest rates for people trying to secure loans. The banks want higher interest rates to make loaning worthwhile.