Perhaps the cart witnessing thing has, as one motive, rewarding those who pioneer by giving them 'easy hours' to make their quota??? It's sort of like 'doorstep Bible studies', child baptism, etc., done to pad the stats??
We all remember that 'hierarchy of worthiness' that exists in the Witness world, with just being a normal publisher (shamefully) at the bottom. This 'special service' of 'Metropolitan Witnessing', like those who rate getting invited to the Annual Business Meeting, Gilead graduations, etc., will add one more rung to their already crowded hierarchic ladder. It makes the ones chosen feel even more special as well. Then it will be viewed a 'new light' and one more step in Jehovah's earthly chariot being on the move. Looking at it from an in-house perspective, it's a win-win development.