Seatbelts.
The cops conduct these seatbelt sweepstakes as a way of "profiling". They've found that these violators very often have other violations, too, if they can find a way to look into their cars.
As far as the "base" system goes, there are stages to everything - especially that. With all due respect, there may be one exception.
Prostitutes. I've heard that with prostitutes there are no "bases". That may be why you either scored or didn't, but didn't "go through the chairs", so to speak.
Hope that helps.
Arf