Central bank lending is collateralised with liquid, tradable securities. That's why the rate is low(er). Furthermore transactions are in large size, so the cost

Central bank lending is collateralised with liquid, tradable securities. That's why the rate is low(er). Furthermore transactions are in large size, so the cost of overheads per $ borrowed are low. If private persons are wanting to borrow a billion at a time and have appropriate assets to put up as collateral, then ok. Central banks are not in the business of retail or micro-finance. The clue is in the name...