Because, like anything related to criminal checks, all they prove is that you *haven't been caught* before.
By definition, every criminal on the planet was in that state at one point in their life, and many of them managed to commit multiple crimes before they were actually caught.
This is how you end up with celebrities who go 30-40 years without a criminal conviction and then it all comes out many years later quite how much they've been doing. It doesn't mean that they were ever very nice people at all.
Biting the hand that feeds IT
