Its rooted in the fact that this behavior is illegal and managers are explicitly trained to not make any such communication.

By your reasoning everyone who reports a crime should be presumed to be lying.

We do in fact require more than a report before meting out punishments. Whether that means "everyone who reports a crime should be presumed to be lying" or "everyone accused of a crime should be presumed to be innocent" is a matter of how you want to spin it.

There's a material difference between a public, open forum and a court that can mete out punishments. Though people tend to confuse the two these days.