What do you mean why not? If a forum embeds an image from imgur and imgur ceases to exist the image stops working. It doesn't matter if archive.org has a copy,

What do you mean why not? If a forum embeds an image from imgur and imgur ceases to exist the image stops working. It doesn't matter if archive.org has a copy, you wont be able to see it without manually going to archive.org to find every image by its former embed url (which likley isnt archived as thats a different url to the one you see on their site).