You can be part of the solution
Every time you go to the airport, you see the six people breezing through the PreCheck line and think, "Man, I really need to sign up for that." Like you say you need to paint your rec room or do your 2011 taxes.
But your rec room is your business alone. Shunning PreCheck hurts everyone.
TSA intended PreCheck for the tens of millions of people who don't need extra screening. When those people are in one line (that moves at maximum speed) the regular line also gets substantially shorter. Without PreCheck, you're just making the slow line longer, more onerous. Think of PreCheck as your good deed for safe flying and speedy airport entry, even if you rarely fly.
Why don't more people sign up?
The only thing Americans adore more than kvetching is making excuses for why they can't change their situations. For PreCheck, these excuses include: the time it takes, its cost, the weeks-long approval process, and paranoia over registering with a federal agency. Pretty much all of them are bullshit.
Don't wanna shell out the $85? PreCheck is good for FIVE YEARS. That's $17 a year. Even if you fly just once a year that's less than you'll spend on dinner for two at the in-terminal Wendy's.
Don't have time to go do the interview? C'mon. A trip to the airport to interview might take you half a day. If that's four hours, and it saves you having to wait on two two-hour TSA lines, you've now made that time back. If you live in Chicago or New York and the airports are all-day excursions, then just schedule your interview for the next time you're flying back home from somewhere.
Approval takes too long? Sign up now and you'll be PreCheck-ready before the fall. If you'd thought about it over the holidays, you'd be approved for summer. The approval time is a constant; the lack of planning is your fault.
Don't want the FBI checking your background? Well, if you've got a previous conviction for illegal toucan smuggling, you won't qualify anyway. If you've got a clean record, showing it to the TSA isn't exactly tipping off Big Brother. It's just one federal agency sharing info with another, hardly a revelation.