Depending on what people do, the government already has their fingerprints.
Personally, I work around schools so I had to get a background check and fingerprinted for that. I also am licensed to handle explosives, both federally and at the state level. I been fingerprinted for that. I've gone through TSA for hazmat endorsement on a commercial driver's license. That needed fingerprints and a background check.
Getting fingerprinted to get through airport security is the least of my privacy concerns.
But my threat model isn't the TSA. They aren't a concern of mine, although I do opt out of their facial recognition.
I am concerned with internet surveillance, corporate surveillance, and communication surveillance.
When I got fingerprinted for my classified security clearance I told them that due to my psoriasis my fingerprints were blank due to the thickened skin. They said it didn't matter so I have a set of blank prints in the fed files.
Sorry for devil's advocate here because I agree with you but hypothetically the answer would be verification. ie., Google already has your password, so why would they need to ask you for it when you log in?
Clear Blue is like this, but they use your iris scan. You have to scan every time to skip the line. But the TSA precheck just fingerprints you once when you sign up IIRC