Do they ever actually analyze the situation? In my experience they just ignore any issues and hit "approve" and on you go. I could have done that myself.

It's a classic false-positive problem. Most times when the self-checkout clerk has to give you attention, the problem is stupidly innocuous, so they blindly approve, as they have been trained by the system that it isn't a real problem.

I'm sure plenty of things get by them this way.