The door-to-door work is busy work. For decades it was emphasized as a way to make money. Print literature, have the publishers pay for the literature and then have them possible get back their financial overlay by the money received from the householder. As long as the publisher paid for the literature the Society got it's money, whether it was placed or not.
Now they can no longer require a fee for the literature from the publishers so they are spending money to print it and not getting money back.They need to find a way to get money and keep the publishers busy. Carts definitely can keep a person busy but they can't have everyone do a cart. If they can get free labor from construction and give pioneer credit or make up a new term so the construction workers feel special, they will do that also.
Door to door work might change to offering only tracts or highlighting the website where the householder can download the literature and that won't cost them much money. I don't see them getting something to replace door to door as what else can occupy so many people for so long?