DHS/CBP is out of control from the ordinary citizens, and neither Congress nor the courts have been eager to limit their ways beyond what is already in limited play. They were engaged in racist and sexist profiling for decades -- as evidenced in strip searches of innocent passengers on arrival to the US -- and nothing was really done to even publicly validate those decades-old practices of subjugating minorities and females for no good reason particular to the individual.

Why a printout is more trusted than an electronic version of a ticketed itinerary comes down to ignorance and some kind of misplaced reverence for ink on paper -- the printout is more readily doctored by more people than a digital version of an eticketed itinerary.