The simple answer is impeachment opens the left up to discovery by Trump lawyers. Why isn’t this discussed.
Trump doesn't need discovery. He just needs to declassify what he's already discovered.
An impeachment trial gives him the forum he needs to capture the attention of the American people and present the truth of how he was a victim of an attempted coup by putting the evidence on display. That is why an impeachment trial will never happen. She doesn't have the floor votes required. And furthermore, the last thing that Pelosi wants to do is to let him show America just how persecuted he's been for the last 36 months and an impeachment trial would turn him into a sympathetic figure, especially given the "no collusion, no obstruction" clean bill of health he received from the Muller report.