Because democratic voters at large don't believe that the USA are in some sort of civil war where it is of utmost necessity to cheer on their team. Voting on election days is the only thing that ultimately matters.
Trump's messages are also very simple to understand. "Grab them by the pussy," that's what a lot of Trump's supporters want to do too, but political correctness has turned the USA into a country where that is frowned upon, hence why it's so important to make America great again. People long for the days when women were more property than human, and black people knew their place in the bus.