IANAP(I am not a psychologist), but I think this is driven by perceived value.
Questions may not have as high a perceived value, because on their own, they don't accomplish much. When you are looking for help, how much would you value a question with no answer? It doesn't help that 10 other people have the same problem, but it sure does help all 10 of ...
"Hot Questions List is optimized for bikeshedding questions..." This was an easy question that got 10 answers in about 10 hours according to timeline.
At our site this means it was doomed to get into hot list and gain multiple upvotes from entertained visitors from Stack Overflow - which in turn made it stick in the list for quite long time gaining even ...
While questions are in many ways more valuable than answers, answers are:
More immediately valuable—they provide a solution to a problem after all.
More easily identifiable as valuable—that immediate value is easier to see.
Teaches more quickly. Questions may be the bigger teachers in life, but answers are more often going to teach you something new in the ...
StackExchange uses voting system to make good answers go all way up and bad ones all way down, not to give rewards and reputations to people. (And a reputation system is perhaps a way to rate users as well as give them permissions based on their reps)
Upvoting/Downvoting means this vote is useful/not useful