As the sidebar says, it's recommended to include your model but not a rule. I like to think this is first and foremost a community to share the images you've generated. I'd hate to scare off potential posters by putting up strict requirements.

That said, of course I wholeheartedly endorse the sharing of models and prompts. For my own posts I like to put the model in the title and include the prompt in the body. It's easy to do for Midjourney because the prompts are usually quite small, but I can imagine it can become quite a chore for some of the more complex workflows.
Though I tend to skip prompts and models when it's just a one-off comment in someone else's post.

On a side-note, this my 1000th comment! 🎉

Most are happy to answer if asked I've found.

Not a mod so I can't say why it's not required but I can say I'd probably post less if it was. Mostly because it's a pain to provide it every time.

I have noticed that including what model I used and at least the prompt if not the story of how I got the results I wanted gets a better response than throwing a picture out there with a title alone. I have a keyboard shortcut for "In Bing Image Creator, DAL-E 3 Prompt:" and I've gotten used to copy-pasting my prompt from Bing after that.

So, I think that asking about the model and prompt if it's not included boosts the community feeling here, but if it were required it would be frustrating and would chase people away.

check out civitai for prompt ideas & more