You're absolutely right that they dont fight dirty enough. Hiwever, I'd say that Democrats lost largely because Kamala was too cowardly to distance herself from biden and his awful policies. She lost because she chose to court moderate Republicans (who gave her the finger and voted for the fascist. Big surprise!).

Biden pardoning his loser son does nothing for the most marginalized folks who will have to deal with Trump's fascist regime in the coming year. It's not a good look that the only time Biden "fights dirty" is to serve his own interests.

Democrats are also willing to fight dirty to win at all cost. They just did

You are confused what winning means for them. It is not forgiving student loan or raising minimum wage.