The similarities between the Kavannaugh hearings and Nordham's situation are superficial. While both of the transgressions (alleged, in Kavannaugh's case) happened thirty or more years ago, the assault charges against Kavannaugh are significantly more serious and a lot less easy to excuse, as there was an alleged victim making the accusation. None of the accusations against Northam concern illegal behavior. In addition, appointments to the Supreme Court are politically significant for the entire country, so it would make sense for the partisan opposition to be more intense.
I believe the alleged similarities involve the rather obvious political partisan motivations of the contending parties, and not the specifics of the accusations themselves, on which you chose to focus.. Nordham's offense involved no legal issues, but a crime against the exaggerated group values that have increasingly become the core of Democrat political values. In the "normal" public court for such offenses there is no acceptable defense. I don't happen to agree and believe the two decade old act did not merit the overturning of a public election.
The case against Kavanaugh did not involve any criminal accusation of a crime by any public jurisdiction. Indeed even after the testimony of the unfortunate accuser, and the denials of the witnesses she said were there, and the largely laughable accusation from the inevitable "me too" accusers, there was no body of evidence sufficient even to press charges. In short there was no "legal" issue.
Your allegation of a criminal distinction between the two was without any merit. Without a conviction or even sufficient evidence to press charges (Not to mention a not very credible witness both of who's cited observers denied any association with her story) there is only innocence.
The common element was the obvious political partisanship and advantage seeking behavior of the affected political parties and supporters.
I suspect the main reason Democrats will not in the end seek to displace Northam involves the subsequent accusations of sexual assault issues against the Lt. Governor. ( they are somewhat similar to the old accusations against Kavanaugh but the reported details involved a good deal more real assault than those involving Kavanaugh. That leaves the Democrats with the prospect of a worse situation in the event Northam is displaced -- no net gain for them.