A democracy derives its legitimacy from voters. When elections are won by tiny margins, but huge numbers of people don't vote then there is a problem.
US turnout is below 60% for presidential elections and has been since the 1960s. If even 1/10th of non voters showed up, they could be decisive in many states. While some organisations trying to drive election turnout are trying to win the elections for their side, organisations that declare themselves to be officially non-partisan such as ACLU also run these drives.
Low voter turn out is considered a problem in many countries. Particularly if that low turn out is driven by demographics. UK
And it's also an attempt to oppose voter suppression tactics, such as those documented in Netflix's The Great Hack.
