They can’t wait until the next nomination to start digging up dirt and coordinating accusations. They need “credible accusers” for everyone on Trump’s list, AND collaborators for them. And everyone must be trained up on day 1 of the senate “trial” and prepared for questions from the press with compatible answers. And the press must be trained on what questions to ask and what details to declare “off limits”.
If Amy Coney Barrett is the nominee there’s extra complexity (not an “old white guy”) so everything must be scripted very carefully to not turn off anyone who’s default position is “support women”.
They aren't waiting until the next nomination to start digging up dirt. They didn't wait for the Kavenaugh nomination. They just needed to find some cast members to assign the parts. It isn't that hard to do in any active life, especially if you have a payroll source with an unlimited expense account.