The down vote process asks people to consider leaving constructive criticism, but it isn't required. Sometimes there's nothing significant about a vote other than someone, somehwere on the internet didn't like the post.
or a cat is operating someone's browser and can't figure out how to take the down vote back:

Other times, there's an obvious link to:
A) not enough research shown
B) not enough specificity
C) several questions being asked
D) just not a useful question in one person's eyes
I don't think your answer is nearly as bad as the question. Maybe people felt virus total is spammy?