You're misunderstanding. What's preventing me from finding someone on Facebook who looks kind of similar to me, finding out their address and phone number, and then claiming I'm them but forgot my ID? Or if I'm a serious criminal planning ahead, applying for a legitimate driver's license in that other person's name with easily-forgeable documentation that less strict DMV's accept when they aren't RealID?

That's what they're guarding against. There's is no secure enough visual or computational ID check that takes a second when you're not already carrying a RealID or passport, that's the point. They have to start getting a bunch of information from databases, determining if it seems like a real person, and quizzing you on information you should know if you're the real you, and seeing if it all adds up or not.

If you are able to follow simple written instructions and enter several pieces of information on a keyboard in less than five minutes... why would you work for the TSA?