Pelosi refused to put the Bush Admin on trial for lying about WMDs in Iraq and now she's refusing to put the Trump on trial for his obvious lies. And the Democratic Party is falling in line behind her.
Whose side are the Democrats really on when the Republicans can lie and obstruct justice and the Democrats are trying to find a way to handle it in a way that doesn't offend the offenders.
I think Ms Pelosi is being politically prudent, rather than attempting to not offend the offenders. There is no point in putting tRump on trial (i.e. impeachment) until at least a portion of Republican lawmakers can be convinced of his wrong doing. It took substantial effort over many months before there was any Republican disenchantment with Nixon. Hopefully, the Mueller Report will be a stepping stone towards impeachment.
My guess they are playing what they see as a long game. They don't want to tire their voter populace with a protracted impeachment hearing. Especially as they do not control the Senate. The last time impeachment proceedings were leveled (Bill Clinton) it did not turn out well at the polls for the party who intiated it (Republicans).