As much as a think pre-check is a scam, I still can't believe more people haven't signed up for it. For anyone who flies even once a year, $85 for 5 years ends up being a pretty small part of the ticket price ($17 per round trip), and makes everything go so much smoother. At all airports I've traveled from I'm door-to-gate in under 10 minutes, even when the regular security line is swamped.

Only thing I can think of is perhaps people live far enough away from an airport to make the interview requirement a burden... though in that case you can try to schedule your appointment for a couple hours before a flight, when you're already planning to be there.

(Of course, more people joining isn't in my best interest since I doubt they'll expand pre-check staff all that much...)