The Dems did not want a stimulus bill that would pass in the pre-election run up. Why would they want checks to go out to citizens signed by Trump? Their bills were unpassable.
So McConnell could send it to committee for markup, and they could have passed an updated version which would then need to be again approved by the house.
Yes, there were a lot of “wish list” items, but that is part of negotiation. I get why you would say the Dems didn’t want a bill that would pass, at the same time it is a shame that is not a theory we could actually have tested. I’m not sure how you can say it was the Dems who didn’t want another check from Trump when republicans didn't really support that idea at all over the summer. The thing they seemed most interest in was liability protections.
Again, I am not saying that Republicans are all bad and democrats are all good. I do believe though that the republican answer from April through December was pretty much to not do anything other than what we already passed and see how things play out. Maybe that is something you agree with which is fine, but, the answer to the question about why there wasn’t a plan earlier is that the democrats were throwing money at the problem but McConnell was taking a wait and see approach.