Yeah - I don’t even cary cards with me any more, it’s all on my phone. Including many store cards (Coop, Texaco, Shell, McDonalds…) which automatically pick up without me doing much - I scan, it works.
The only thing I can think is that the US is such a fractured environment with Federal, State and Local government, each with different jurisdictions, rules and taxation, that trying to get it to work would be beurocratically difficult. But at the same time, it’s so ruled by corporations that surely they’d want to push the easiest way - flip your phone out and wave it to pay, easy and secure, so make it happen :D