Their entire business is predicated on steering you away from using your credit or debit card (better for you) to a direct bank withdrawal (better for them).
Bank withdrawals carry a risk of overdraft fees, have fewer consumer protections, and lack the rewards programs and other benefits of cards. But they cost less for PayPal. Merchants don't pay any less though -- it's how PayPal makes money.
Each and every time it defaults to bank withdrawals. You have to hit "Change" to select your card, every time. There's no way to change the default to your card. The only reason for this UI is to steer customers away from their best interests.