It does not seem like the democrats where serious when it comes to impeaching the president, it was obvious the republicans where going to rig the senate trial and thus even if they have a rock solid case to the senate republicans would still find a way acquit the president. In order to remove the president from office bipartisan support is needed (at least 20 republican senators).
Maybe if they had waited John Bolton would have been willing to testify under oath in the house and they would have a direct witness for a quid pro quo. The republicans in the senate realized Trump was guilty so the didn't want any more witnesses, not even Joe/Hunter Biden.
But hardly any republicans are willing to turn against the president and thus the goal should be to win over the public, the democrats failed with that too,
https://projects.fivethirtyeight.com/trump-approval-ratings/
Maybe the democrats think they can always try to win 2024 but by then the republicans will have rigged the system so hard in their favor they will stay in power and the united states will become a full blown dictatorship, there might not even be any more election if the republicans manage to grab even more power.