I've noticed many JW carts at libraries and other public places but never a JW in sight or standing next to a cart,, and I'm thinking it is because the WT corporation doesn't want the indoctrinated members talking to people that might approach because of all the notoriety child molestation lawsuits. And so I feel to minimize the chances that Johnny kingdom publisher might meet up with apostates they encourage not standing next to the cart(leave it unmaned), with periodic check up so as to count one's time.
BTW I live in the silicon valley where I'm sure a lot are waking up, and I'm sure a lot of manned cart have gotten Witnessed to by apostates like myself(I know I did my share), and so instructions from the CO in our location maybe to not be so close to the carts here.