I am inclined to believe that less people voted because the way in which the election was framed did not inspire them to vote.
We took it for granted because it's obvious to us that 
is unfit, but we didn't do much in the way of rationally explaining why that is. Instead, we used divisive rhetoric and distilled the entire thing down to the same partisan fight that it's always been, and that made it very easy for people to disassociate and tune out.
@kel I am fed up with any and everyone that needs to be "inspired" to get off their ass to vote.
@Eclecticmezzo We too had to be inspired once. ¯\_(ツ)_/¯
@kel maybe you did, but I've voted for the past 35 yrs because it is my civic duty and responsibility. I held my nose and voted for the candidate that was the closest to my vision for this country. Politicians aren't rock stars, we aren't groupies. We had a job to do and over 20 million sat back and said nah you don't inspire me, screw the people that get hurt.
@Eclecticmezzo My point is, you weren't born with an inmate understanding of the importance of voting.
You learned it.
It would be great if everyone learned the same thing. Clearly they did not, and I think it's because we didn't do much to teach them in ways that would resonate.