LC: The issuing bank is the first and the only line of defense. The commitment to pay is from the issuing bank, to whom the demand for payment must be made under an LC (after complying with the terms of the LC).

BG: The issuing bank is the SECOND line of defense. Only if the buyer/payer fails, demand can be made on the issuing bank to pay (in terms of the BG).

Bottom line: Either way, the issuing bank stands committed to pay.