because Cops are always wanting to know who they are interacting with.. heck, even walking down the street they want to see your ID, which in that case, I don't think you have to show them. They are supposed to need probable cause, but they are going to look up and 'run' everyone through their system to see what comes up. It's supposed to be illegal, but fighting the law always leads to escalation and most of the time, they are gonna win no matter what, so most people just do what they ask them to do and hope it doesn't turn out badly.