It makes sense to me. This is a database keyed by facial images. They don't know your name with certainty. The only way to look you up in the database is by face. Then presumably they need the ID to make sure it's you who's requesting the info. Hard to imagine how else to do it, given the nature of the technology.
Exactly. Otherwise, this is just a vector for any person to exploit the process and freely play cop by uploading a photo of someone they're trying to track.
Yes, but the value is to provide that in exchange for money, and ostensibly only to law enforcement agencies and similar organizations. (If you try to sign up on their website, it says "Clearview is available to active law enforcement personnel" and that you need to apply for access.) If you're a random citizen and can get the same data, especially for free, the value proposition breaks. And the privacy implications would be worse.
So, I get why they ask for ID, even though I also get the reluctance to give them your ID since it could help tune their system.