Ticketing people one by one is an inefficient way to spread the word and it builds ill will. Like it or not, many people believe traffic sting operations are focused on fund raising, not public safety. ("So this is how they're going to make up for those $30 license tabs!") Ignoring that perception will reinforce the cynicism and turn people against the seat-belt law.
Read: Seat-belt crackdown doesn't need subterfuge: WSP idea good, execution isn't/Gary Crooks, Spokesman-Review