As I said before, I do think the cart witnessing itself was not a bad idea, but the way the org has implemented it is totally ineffective, telling publishers not to engage passers-by unless they are first approached.
When it was first introduced (here in Europe at least), publishers could offer literature held in their hands, and could engage passers-by in conversation. That seems much more appealing (to those who might be interested, of course) and more potentially effective. Every single street preacher or vendor offering anything in public will approach people, rather than just passively stand around.
However, the org soon changed the 'direction' on how to do this, and now it is much less effective. Supposedly, they did not want the witnesses to seem like just free paper distributors or those intrusive charity volunteers you get on the streets (they're often known as "chuggers" here in the UK - short for "charity muggers" due to their persistent attempts to approach people asking for donations). Although I can see the point of that, they could've just introduce more careful guidance about how to do it. Instead, they basically told witnesses to stop holding literature and not to approach people.
I think there was an ulterior motive. During the months when the original way of doing things was in place, I know congregations were placing far more magazines than they did before the carts were introduced (I mean hundreds more), and many were enjoying conversations. I suspect the org heard about this from branches and got worried about the cost of printing additional copies to cover the demand. It usually comes down to money in the end. If they were really interested in "spreading the good news", then surely they should be pleased about that? They're always quoting scriptures about "liberally sowing seeds because you don't know where they will grow", etc. Even if many copies were discarded, the point is supposed to be about "reaching people".
Instead, they issued orders to make the trolley work far more passive and, as usual, killed what little 'joy' publishers might experience in their ministry. Now it's exactly as you see in that picture: standing around looking bored, hands in pockets or just chatting with the other witnesses around (or staring at their phone). Also, those ones in Barcelona are doing what most witnesses do now which puts people off approaching - all crowded too close to the carts. Even if someone were interested, they would probably be put off by this line of 'cart bodyguards' staring at them as they walk up.