Because humans tend to give things names based on their relation to prior naming conventions. As voting on election day, singular, was common for so long then everything else is in relation to that aingular day concept.
No, a more accurate name will not be adopted because people are used to the current terminology and knows what it means. Just like we won’t switch ‘daylight savings time’ to ‘daylight shifting time’ even though that would be more accurate.
Depends on who she shoots!