Except when they deny you without telling you why, with no real appeal process, because you can't JUST get pre-check, you have to get one of the other certifications instead. The most common one is Global Entry, which allows expedited customs. Have you ever forgotten to declare something small coming back into the country and they find it (even if it's not prohibited)? Then you're permanently banned from this program. Ever had someone ship you something from overseas and accidentally misdeclare customs (outside your control)? Banned. I found out I was banned after paying the $100 non-refundable fee for the latter reason because a seller didn't fill out the customs form properly.
They need to offer a way to only get pre-check without going through one of the other programs.