Many things can be going on, including the hallmarks of partisanship, but let me risk an hypothesis.
I have encountered some people who tied the credibility of doctor Ford's testimony to the guilt of then judge Kavanaugh. They didn't seem to appreciate the possibility that you could logically find both credible, not call either a liar, yet consider the case insufficient to warrant further actions. Their reasoning moved from 'Ford tells the truth' to 'Kavanaugh is guilty' to 'Kavanaugh must be sanctionned.'
If you want an example, Bill Maher made this point on his show last week. I usually find him funny, yet rather reasonable for a comedian, but I think he was wrong to equate credibility with truth and move on to a presumption of guilt.
You can find Ford to be credible without being able to tell if she told the truth, but you have to keep in mind a few things:
1. It is extraordinarily hard to tell if someone is lying. Even body language expert Joe Navarro comments on the ineptitude of investigators to figure out who is lying and who is not. What you can find are clusters of reactions that indicate a peculiar emotion -- but people can react to thoughts, just like they react to event.
2. Witness testimony is the least reliable source of information you can find. Our memory is not a collection of events, but a set of hints we use to reconstruct stories. Given that we are biologically prone to self-deception and might be motivated to see things in certain ways, we easily mix things up without knowing it -- to a point where believe in our self-fabricated delusion.
So, I can say AT THE SAME TIME that Ford gave a credible testimony, yet see it as insufficient to condemn a man -- even just on moral grounds.
And this is where it sticks for some people on the left. It seems like not going forward to punish Kavanaugh is akin to insulting doctor Ford. However, if you rid yourself of the equation they made, the problem vanishes.
Personally, despite leaning to the left, I can't bring myself to hold someone accountable for anything if all I have is one testimony, no material evidence and no ground for believing the suspect ever did something similar in other cases. I would rather let a criminal walk free than to punish an innocent. I don't trust people around me enough to take the chance of being on the receiving end of a false accusation and get punished for something I never did.
Even if I resent some of the opinions Kavanaugh might hold in the future, the man deserves the benefit of the doubt, certainly is competent enough to do his job as a SCOTUS Justice. It's important for people, left and right, that a final arbiter exists to settle disputes, least they degenerate into violence.