My guess is it's an attempt to improve morale and create an encouraging narrative for the Democrats, like a coach telling his team, "we're gonna beat these guys!

You might think going with "our democracy is in danger! Get out and vote!" would be more effective, but years ago I read about a study in which they found people were less likely to vote if they thought their side was going to lose.

Of course, I've seen the "our democracy is in danger!" narrative quite a bit, too, so maybe they're just throwing everything they've got at the wall to see what sticks.

Edit: Also, you may have noticed that a common technique the media uses now is to go with a headline and first paragraph that pushes the narrative they want, then bury the actual contradictory facts somewhere near the end of the article, because most people only look at the headlines.