Yeah, but this one time, at band camp, Trump made a mean phone call to Ukraine and got impeached
You're leaving out a very important detail: part of that phone call was specifically about Trump requesting Ukraine's help in investigating the Biden/Burisma links and corruption. Clearly Biden, if not the whole Democrat leadership, knew such an investigation would expose at least Biden - and maybe more people. The evidence is clear now, as more and more people are coming forward and more facts see the light of day.
THAT is why they went into full attack mode. Trump was sniffing around the tree, and that had to be stopped. And when I say full attack mode, I mean across all fronts. They had the House, the Senate, the State Department, the CIA, the FBI, AND the full breadth of the media attack, attack, attack.
The idea was clearly to overwhelm the nascent Burisma/Biden corruption narrative with the "impeach Trump" narrative. And it mostly worked - they got to impeach him, get to the end of the term with no Ukraine/Burisma investigation, and select and install Biden as President.