It's all for billing purposes. If you're not paying your bill they have more info to skip trace you and collect the debt.
Also, it's designed to cut down on insurance fraud i.e. using/stealing someone else's insurance coverage.
I'm no fan of showing ID to anyone, but in this case it is due to private business practices, not the federales tracking our CT scans.
We can only be kept in the cages we do not see. - Stefan Molyneux
You are a function of what the whole universe is doing in the same way that a wave is a function of what the whole ocean is doing. - Alan Watts