Going thru security last week after customs at DTW I forgot to take off my shoes. I said I had gotten so used to PreCheck and wouldn't it be nice to have it here. The TSA agent replied that they had tried it for a very short time but that so many of foreign boarding passes couldn't or didn't print the special bar code that is just caused too many problems.

That I could see -- people arguing "but I have PreCheck" when being denied the lane because no barcode on the BP. Hell, I'd be one of them