Gorsuch was not a painful change for the left. He was replacing Scalia, and so that kept status quo. But Kavanaugh is another matter to them because he is replacing Kennedy, the swing vote of the group. Not only is there more urgency to stop him, but there is more urgency to de-legitimize him if he gets on the bench. Moreover, their base demands that they get in the mud and do whatever is necessary to stop this nomination from happening. If the Dems don't, they will hear it from their base.
That's why the Dems are scouring Yale and asking for people to come forward. That's also why they are helping people remember important facts that they forgot, like that Kavanaugh did it and not someone else.