Because it's War!
Voting is a Martial act. A revolutionary act. Every Vote we make as an American (or other) citizen is a declaration of War on tyranny. Regardless of the candidate elected, democracy wins against authoritarian regimes, monarchies, despotism, fascism, communism, oligarchies, and dictatorships.
You can see it at the voting booths. Doubt about the outcome, desire to be on the winning team, consternation about the lack of decent choices, hope that whatever happens, they'll be alright...
It's not the same as facing bullets, but the war rages on.
Now, what about other countries? What day do they vote on, and what does that tell us about how they perceive voting? Is it just America that has a Martial attitude about everything governmental? Are there any countries that vote on Fridays?