Because the bad guys are known for presenting flawed boarding passes to call attention to themselves? Or ones for the wrong date or flight so they will be thwarted from getting on their intended flights?

Surely DHS doesn't believe a terrorist cell competent enough to create, conceal and carry binary explosives past the checkpoint is going to "forget" to have a matching ID and accurate boarding pass?

WHAT SELF-RESPECTING TERRORIST IS GOING TO BE CAUGHT BY THIS HURDLE?

That's why it's offensive to thinking people that TSA presents this as one of the many layers of security. We are not as stupid or shallow as you think we are. And neither are the bad guys. Yet you waste resources and our time with the doc check charade.

The inconsistency in the process from airport to airport isn't "intentional variation" to keep the bad guys on their toes. It's an admission that the process is theatre, and the scribbling/stamping is merely rearranging the props on the stage.