If we look at this from a game theory perspective it actually works in their favor. People want to make lots of money, if they lie they're going to lie about being paid more and not less. If enough people lie to affect the overall statistics, then everyone is going to be pissed off at their management for not getting paid as much as everyone else. At this point management has two options: reveal the actual salaries of everyone, to prove that actually everyone is getting paid less than what the stats show (oof), or keep the salaries hidden and deal with a workforce in which every participant believes they are chronically underpaid. Neither of these options are good for management, and the only way out is to hand out generous raises.