There are multiple potential explanations. I think disallowing commerce without an agreeable substitute, like immediately transferring or escrowing money from other accounts, is an unacceptable inconvenience. Often times, a person wants the protection of a credit card, while having sufficient assets to purchase in cash or repay the card corp. If anything, that a debit card lacks similar protections of a credit card is absurd and inconvenient per skimming and missing fringe benefits like travel insurance.