You make a few assumptions which are not correct. I did look into the cause of it and uploaded a new image to the article on the site. I looked into how Twitter and Facebook associate images and see that they do not update their images once the tweet / post goes out. On the Facebook end I purged the cache on the developer site for the link and see the updated image but the post for whatever reason doesn't update. Maybe it will later or maybe it won't, that's something that's on the Facebook / Twitter side that I don't control.
Now, why don't I just delete it and re-post it? That may be 'better' according to you but for me it isn't. The post already went out, people have commented and liked, retweeted, whatever. The "damage" of the post has already been done. It would be pointless, redundant and a bit confusing to re-post the same article link. Some people are offended by the image if they just look at it on the surface (no one has actually said that they were) but if they click on the link they will see the context.
Also, I'm busy with other things so it was not a high priority but the rude way in which the change was demanded made it an even lower priority.
"Now, why don't I just delete it and re-post it?"
David Tseng, Today at 4:00 AM