A lot of this consultation stuff - local residents haven't heard of something but some interest group has - this is because to most people transport planning is pretty dull. It's some spods discussing timetabling or junction design or traffic light prioritisation. So when Lambeth are consulting on their transport policy most people just aren't interested. But special interest groups are - because it's what they are interested in. They are often working away in the background for years, helping to push for incremental improvements and lots of things that barely get noticed by most people. I'm a bit of a transport spod - I follow things sporadically and from a mostly layperson point of view. I read the lengthy London reconnections articles about bus route rationalisation or the Uber court cases or Thameslink upgrades or whatever.
Most people find all this stuff really boring. But occasionally something happens and suddenly people who were never previously interested in the bigger picture of transport planning are paying attention. LTNs are one of those things. Certain people are paying attention because it now takes them somewhat longer to drive somewhere. The same people haven't been paying attention to the gradual cuts in funding for public transport in London that have been going on for the past few years, or at least they haven't been staying Facebook groups about it. The fact that they have never been interested in this stuff before means that they think LTNs are a wacky new idea, not a fairly conventional and well established method that's been used for decades. It means they don't have any alternative solutions to offer, because they haven't already been thinking about it for years and watching the things that do and don't work.
I am rambling a bit. What I started out to write was a partial explanation for why you see this situation where it appears that the council has been talking to lobby groups but not local residents. When actually they have been talking to those people who are actually interested. It's not a sinister conspiracy. It's just that if you are talking about the bigger-picture, long term stuff, not the immediate 'shall we put a traffic filter on your road' stuff, most people just aren't interested, and think it's desperately dull. I've seen eyes glaze over myself...