So much complexity, so many third parties you have to rely upon to not make any mistakes (or be abusive), for the convenience of not carrying a slip of paper in the glove box of your car....
I don’t want cash, a wallet, plastic cards, metal keys, or tons of slips of paper from receipts and all other kinds of bullshit.
Putting it on the phone as a native app is hardly complex. Use QR codes, an officer won’t need to look at your phone