Are they, necessarily? This could be entirely up to expected value and cost/benefit. Right now, current day, on average, the amount of power and attention wielded by a woman making an accusation of sexism is far larger than that which would be wielded by a man. This gender skew in outcome causes the cost/benefit calculations made by advice givers to also be gender-skewed. As a result, women get one cost/benefit calc, and men get another.
The problem is precisely systemic societal inequality and sexism. It's sexist to automatically value the word of one gender over that of another. However that is essentially what our society does in this context, made worse through social media's amplification of the mob mentality. It's this amplified societal gender skew which is the problem.
The way out of this is to value and respect evidence. The way out of this is due process and the concept of innocent until proven guilty. The way out is through principles which we know can counteract the evils and dysfunction of the mob, which we have known and codified, and whose value has been borne out by history, since nearly a millennium ago. Only this time, let's apply these gender neutrally.