It’s so people can trial having digital IDs. Some TSA and others can scan the new IDs, but not everyone can. So in the meantime, you have to carry your physical one too.
People are pointing out potential negatives, but this has some good possibilities for privacy too. If you show your ID at the liquor store, there’s no need for the clerk to know your name or address. The scanner can just verify your age.
It’ll take so long before you can even leave your physical ID at home and count on everyone accepting your digital one. And it may never happen that people stop accepting your physical one.