I personally think the carts were a brilliant idea. The Watchtower recognizes that they don't need to speak to anybody at all to keep things going. The money comes in from existing members, not from the public. Therefore by having the carts, the money keeps coming in, the hours spent on preaching go up, because it's super easy for Jdubs to rack hours up. JWs don't actually engage anybody at a door, so less chance of conflict and bad reactions. Jdubs that hate going door to door, are more disposed to standing next to a cart looking at their phone, so they will preach more.
The only curveball with the carts is that it exposes them to apostates more easily, but even this is not so much a problem, because they just pack up and leave.