In my opinion it could be a number of different factors. Maybe there is a flaw in their screening process, or maybe that 70% is just because of the sheer amount of applicants per year.

CBP is the largest law enforcement agency in the nation; they likely receive tens of thousands of applications per year, and that could definitely lead to a higher number of disqualified applicants.

Sample size makes a huge impact when talking about percentages.

Polygraphs are nothing but pseudoscience. The results are largely open to the interpretation of the examiner. I personally know guys who failed CBP’s polygraph after being accused of lying about whether or not they’ve engaged in terrorism against the United States.

I’m not against using polygraphs as part of a background investigation; but I feel like it’s only use should be as an interview tactic. Results should have no bearing on employment as long as the applicant hasn’t admitted anything disqualifying.

CBP has a lot of trouble with staffing, partially due to the fact that ~70% of applications fail the polygraph exam during the background investigation.