They may have underestimated how important traditional door to door ministry has been in structuring JW life, self-understanding and commitment. Over emphasis of cart witnessing threatens to undermine that.
Any thoughts on how much people doing at either broken apart? Is cart now a larger portion of the work?
Door to door is a more consistently active activity than sitting at a cart. You're typically on private property, and it is similar to territory sales. You have to be ready for anything. However, as history progressed (50s through 90s), the activity became more conventional. Probably directly correlated to born-in JWs learning it as a more cultural activity rather than converts doing it with apocalyptic passion.
Again, the one street of territory + break + 3 calls was a routine I remember well. Nothing close to the "preach the word" urgency WTS made it seem like was going on.
To get to the OP, I would say that cart witnesses has the potential to lower the bar even further. Just sitting at a cart in a boring location? I've done table events before in past jobs, including major event centers with lots of people. You have to be standing, you have to invite people in, you have to ask questions constantly. It's actually really hard to do well.
But it's also really easy to do poorly. Sit behind a table and not say much, barely anybody will approach you. And that's in a busy location. So in this light, it may be an even bigger excuse to non activity in the ministry, which although it's never verbalized, appeared to be the primary goal for most of the JWs I personally knew.
In private, I remember so many JWs saying they hated the ministry. If there was a way to cheat at it, they would. All of them dreaded to be in the car with one of those 70 year old old school Knorr Era witnesses that wanted to knock on 100 doors.