APT Margin Transaction Losses, page-17

Most people use credit cards because its easier than paying cash. Noone wants to pay 19.95 for an item and carry around 5cent pieces.
Cards also have the benefit of rewards points, as well as statementing all your items for look through at the end of month.
Cards also can be used online for instant transactions where as other payments cannot.
The people that use credit cards for the actual "credit" facility (i.e. pay late), incur 20%+ annual interest rates

Payment methods have been expanded in recent years so that now you can use your phone (linked to a card/bank account), or other similar methods. This is sometimes preferred because the phone is becoming an electronic version of your wallet.

The only added benefit afterpay has over these others is that it allows you to a) get credit without a credit check, and b) pay for your goods over 4 installments rather than upfront. Both of these appeal to the least credit worthy people in society and as such its a fair assumption that it is used by the lowest earning demographic