The work of processing a credit card transaction is 1/100000th the work of a blockchain transaction via proof of work. Credit card transactions can get enormously impractical and it will still be more practical than a purposefully-inefficient distributed database.

Most of the stablecoins are on Ethereum, which is Proof of Stake, and the remaining is on centralized chains like Tron.

Gas fees on Ethereum L2s like Base cost $0.0016 to send USDC, and $0.00064 to send ETH.

Stablecoins don't use proof of work.

how are cards impractical?