Every now and then I used to run into someone who'd been waiting for us to knock on his door, the kind of person who'd studied up on JW doctrine and relished the confrontation.
I always wondered whether it was worth their time and effort, all the study and memorization on the off chance they'd get a JW knocking on their door who wouldn't run away at the first hint of "apostasy."
These carts change the dynamic. It's now a lot easier for those who are so inclined to seek out the witnesses and confront them. Just based on my experience, I'd guess a large percentage if not an outright majority of people who approach the cart witnesses do so under some pretense, not because they have any actual interest. If I were still a witness I'd just as soon be out door to door where at least you can run away. There's nowhere for the witness to go if someone confronts them.