Maybe they could promise to make the rent lower. Or to make abortion legal. Or to stop bombing 2 million brown children in the Middle East. Or literally anything people actually want, instead of running on the singular platform or "obviously they'll vote for us because we're not the Republicans". People are getting really tired of the latter. Notice every time a candidate comes out who actually promises things people want he wins by a landslide?
They actually have offered policies along this line but their messaging is weak at best.
It also competes with an opponent (the GOP) that is more than willing to outright lie to sway voters. This isn't to say that the DNC is beyond reproach but we're way past "both sides" at this point.
