Maybe because you do not understand what we are writing here either...
You create this false dichotomy as if if we use slang and other local expressions that therefore we do not care about making our comics accessible. This is simply untrue.
In works of fiction, there is always a tension between show and tell. What you are arguing above is pure tell. You are saying to creators, do not let your readers guess, tell them. Do not show them the context of terms they may not be familiar with; avoid them entirely. And if you do, you care about making your comic accessible. But if you don't. you obviously do not care about clear storytelling. And that premise, not matter how much you argue above that you are not dictating or painting the word black and white, is exactly what you are doing.
Fiction is way too nuanced and a fun playground to abide by the rules that you suggest. Are you telling me that Hemingway, Atwood, King, Updike did not care about making their work accessible and totally avoided complicated terms in all of their work?
Your position is not well thought of. It is well-meaning, but in practice, way too restrictive for anyone who wants to engage with modern literary works.
Here is an example of what I feel is important about accessibility and that can actually affect readers' understandings. When not too corny to have the characters introduce themselves with their names or address others by their names, especially in new scenes or ones where someone has not been seen for a while.
Why? Because, understanding the web comic format, I know that there are gaps and that readers may skip pages and not recall every character the way I do. So I need to reintroduce them once in a while. it is the same thing that film makers do when shooting an ensemble sequence. While they may focus on two speaking characters, from time to time, they will show reactions shots of the other people around, and even of the setting to remind us that we are in a mall, or an elevator and that they were two women in the elevator witnessing the exchange between the two main characters.
That is more important to help the reader follow the story than avoid using an unfamiliar term. They can search for a definition of an unfamiliar term but they will have more problems understanding the relationships of two characters that are interacting that we haven't seen in the last 20 pages of the comic, or in practice, in the last 20 weeks.
Now, this is an issue about accessibility that I care about, and again, the people who trained me about fiction writing put a lot of emphasis on this point rather than how I use vernacular terms.