Most of the users are either forgetting to add the exclamation mark or maybe deleted the exclamation mark before posting the question/answer.
That's not what happens (at least not in most cases); new users are not allowed to post images on some sites: Which SE sites require 10 reputation points to post images? because it has led to abuse in the past.
New users aren't able to post images (to prevent spam or abusive material) and their posts often end up containing
links to an image: some text here
(source code: [some text here](https://i.stack.imgur.com/99gX9.png))
bare links to an image page like this: https://imgur.com/a/bDrTcpm
The first case is easy to solve: just put a ! in front of the opening ...