Tap to pay may work if you actually use your phone as your wallet. From what I see around me, most people don't. And on this website in particular you have surely seen people advocating for cash over privacy concerns. Nor would I be confident that my card will work flawlessly in another city half a planet away before I get there. I will buy a weekly pass from a machine, though, especially if it looks cute enough that I can bring it home as souvenir.