Soooo many people don't bother following the simple instructions filled in automatically for alt text (old stats). Posts are rife with "enter image description here" which leaves content inaccessible for the visually impaired.
I realise that in many cases we cannot prevent this — lazy peeps will be lazy.
However, if we block post submission when images are present with "enter image description here" and prompt people to provide real image descriptions, we may improve results by some percentage. Sure, some will just try to enter an empty string (block that too!) or some meaningless nonsense. But surely others will go "ah, okay, I should do that".
Worth an experiment?