Debit cards has orders of magnitude less fees per transaction. You might be fine paying 3% of your money to credit card companies but a lot of others would be fine with a debit card. The US system makes everyone share the burden of paying for credit cards, but in Europe they can't do that so people mostly go with the much cheaper debit cards.

Some people can't have credit cards bc they're not us citizens or permanent residents.

Some people can't control themselves.