The question is one of trust. If I tell an officer who pulled me over, I don’t have my drivers license, but here’s a picture of it on my phone, it wouldn’t go well. How does he know I didn’t retouch it? Or I took a picture of someone else’s drivers license and change the picture?
For a drivers license app to work, it must be approved by the government. It must have a way of detecting that the information is accurate and hasn’t been tampered with.
And trust works two ways. I don’t want to hand my phone to a police officer where they can start pursing my data. The phone must remained locked while displaying the data. Even better, the officers can scan it with a device while I hold my phone. Like the way you can pay with a digital credit card on your phone without handing it to the store clerk.
Apple could have always made softness to store my credit card and maybe scan it in, but that Secure Enclave was needed for Visa and MasterCard to consider working with ApplePay and making the whole ecosystem work.