The watch is on my wrist, or the phone is already in my hand. The credit card is buried in a wallet that needs to be taken out of and put back into a pocket.

Also “unlocking” isn’t an inconvenient step, on iPhone it just happens automatically. As it should on android if the fingerprint sensor is in a convenient location.

Umm, assuming you have the same opinion as grandparent comment, you don't want google tracking your payments but you'll happily trust google's pinky promise about your fingerprint being stored only on the phone?