The last 12 times I've flown in and out of FLL the past month or so, the pre-Check line has had just me in it and a couple hundred people in the normal line. I don't get intimidated by crowds easily, but when it's between 0530 and 0600 and everyone is already inherently grumpy from getting up so early and they see one guy "cut" the line, it tends to make people grumble.
Flying out of MIA, DEN, LAX, JFK, and SFO I witness the same thing. Granted my sample size for time is small, but during what I would call peak times. Even going out of ATL, with the hoards of possible pre-Check eligible passengers, I have never waited.
As I said before, it's sucks when you are eligible and can't get it. But knowing how massive lines can get at FLL, a TSA agent, knowing it's spring break, decided to open up another lane (possibly 2) to increase the throughput of passengers so they are able to make their flight.