By showing that they are serious about uniting the country and moving forward. They lost all the moderates this election. Pardoning Trump would give them some credibility to earn them back.  

 Politics is a short term game.  Democrat calls for unity will come shortly before the next midterms.  There is no value to doing this now.  They will be trying everything to hamstring Trump on every issue (aside from infinite support for Israel) in the short term.  

Note this is absolutely what their supporters want them to do. 

 I’m aware they’d never do this, still think they’d gain more support than they’d lose 🤷🏽‍♂️ 

 Why did you think he wouldn't do this? I know you haven't been a dad for very long, but to me this was one of the more relatable things Biden has ever done.