Apple Pay as Payment Method

Because ApplePay is a payment mechanism, not a payment method.

You CAN add specific cards (payment methods) which ARE in your Apple Wallet.

See more detail here:

Payment methods that you can use with your Apple ID - Apple Support

Apple Cash can be used and most payment methods in your Apple Wallet can also be used.

Note the addition of my Cash App card from my Apple Wallet and the notation it’s Apple Pay.