Exactly. Sexual assault cases are notoriously difficult to prove in court, because the threshold of proof in criminal cases is extremely high. This means that even if a person reports the crime, and puts themselves through the excruciating distress of going over and over and over their experience in open court, and having their story their life picked apart - even then the chances of a conviction are slim to none. Beyond reasonable doubt is a very, very, high bar - yes, for good reason - but unfortunately in sexual assault cases, even where the jury believes the victim, there is often still that doubt that is very hard to overcome. Because as you point out, unless someone else observes the crime, doubt will often be insurmountable.

It sucks. It really sucks - but an adversarial justice system is also not set up well to punish sexual assault. In the 80s, in the relevant state, the crime was a misdemeanor. So imagine the prospect of going through all the above, to then be faced with your assailant receiving as an absolute best case scenario (should that very unlikely conviction ever happen) little more than a slap on the wrist or stern talking to. Hell we're still seeing actual convicted sex offenders receiving pitiful sentences even now.

Justice is rarely a realistic prospect for sexual assault victims, so when people say "why didn't Ford report the crime?" they need to reflect on the fact the overwhelming majority of rape victims do not report the crime for the reasons above, and that even where they do, the chance of receiving justice is almost zero.

But of course, the standard is not beyond reasonable doubt when it comes to Supreme Court nominations. The standard should frankly be any doubt - and Kavanaugh's actions, even without the multiple accusations against him, have proven he's unfit.