Right it is about busy work and control. As long as they are making a profit on whatever literature they are producing, they will continue. I honestly think that they will change it over time to just be the distribution of tracts. I think the next phase is the discontinuing of the public WT and only have the Awake offered to the public.
You have to keep the service piece because 1) you use it to measure a person's devotion to the religion (ie - appoint ms/elders based on the time spent), 2) gives women a place in the organization since pioneer is really the only thing they are allowed to do and 3) allows you to identify people who may be wavering based on their hours.
It's highly ineffective for making new converts but every effective for measuring and controling the flock. Until they come up with something else that accomplishes that purpose, there's no way they drop the "preaching" work.