I think that the (lack of) voting, close voting, editing, and tending the queues are all definitely due to a lack of active users, as both Al and phwd have pointed out. The fact that we have closed questions based on the votes 5 regular users only a handful of times has been more bothersome to me than the voting for a while, to be honest.
As phwd pointed ...
Google changed up the algorithm so drive-bys are actually lower than before (last time I checked a 40-50% decrease)
Also page view count has been decreasing in the past year.
So yes disengagement is there, the incentive for voting is lacking in and has contributing factors directly or indirectly from