I would tend to believe the WTS thought cart witnesses would actually be effective, and that when it comes to their own bs they can be that naive.
My experience in the US was similar to what most on this board say. That pre internet there was little contact with householders. The JWs response? Put carts in public places where there are people.
Ok in cities possibly, lousy in suburbs and rural.
JWs have conditioned the public to not want to talk to them. Easy to forget, but JWs have been around for the entire past century in the USA, much of it with door to door work. They defined the crazy person who wants to talk religion. Most avoid it, because they defined it well as something to be avoided.
JWs will meet defeat wherever they go. The message is outdated and has no relevancy. I think the cart stuff is an inclination how little they actually understand people.