Because HR lies and say the opposite in the majority of companies. "Come to us with any problems, it's safe and anonymous, we are here to help you".

From personal experience I have reported gross treats by senior leadership to an HR rep who was shocked about hearing their HR employee evals being suppressed by only allowing score between 8-10 in a 1-10 score. The HR rep confirmed it personally that it was happening and a few months later appeared on the other side of the desk with the leadership as they fired me for budget reasons.