I already said why. But to go deeper: the US has, and has always had, a strong libertarian and anti-government streak among a very large proportion of its citizens. And it's not going away. That's why the US doesn't have a national ID, the way so many other countries do. That's why adults are not required to carry ID's with them, the way it is in many other countries.
These political values are a strong part of American culture. The distrust of central government and authority has been around since the founding of the country. They belong to the most durable of American values.
If the US still doesn't have a national ID, or require citizens to carry ID's, and there's literally no political movement towards that, what on earth makes you think this will change?
Being able to put a driver's license on your phone is state-level. It's a form of ID we're OK with. It can't be mandatory because not everyone can drive. There's zero slippery slope here. I just want to carry the card I already have to carry when driving or flying, on my phone instead of physically. There's zero downside here.
Citation needed.