It's less bias against women (demonstrated by male accusers of female perps having even worse odds), but rather that it's an accusation of a serious crime and thus has to be proven beyond a reasonable doubt. Which is complicated by very many cases having exactly 2 witnesses (accuser and accused) and often little or no other evidence.

The usual counter to this is to claim that accuser testimony should always be believed and should itself be proof beyond a reasonable doubt because no one would ever lie about this sort of thing, but that doesn't jive with reality - for example, look at the Duke lacrosse case, or Brian Banks, or Tracy West accusing her ex (to use a few that got significant media attention), or those exonerated by the Innocence Project (a majority faced sex crime charges). For the first two of those, the accuser actually admitted to lying, (even if Crystal Mangum waited until 18 years later while in prison for an unrelated murder and Wanetta Gibson waited until the person she falsely accused had served 5 years in prison and was on the sex offender registry and partway through his 5 years of probation and then had to be secretly recorded because she didn't want to reveal to truth publicly and risk losing the damages she was awarded from the school district).

Yeah, because the courts are clearly biased toward male rape victims. 🙄