Why would they unfeature a meme?

I think the most common cause would be if it got a lot of downvotes in a short period of time. Memes like that might be bumped back to submission on the assumption that they contain inappropriate material.

The only other possibility I can think of is a person flagging the meme or giving the mods feedback about it to the effect that in some way it broke the site's Submission Guidelines. If the mod looked at it and agreed, they could pull it.

It's frustrating when it happens.

Thanks socrates you`re my favourite philosopher.Here is the meme imgflip.com/i/x2mr9
I`m not sure how it is inappropriate...

I can't really see any reason why it would have been bumped back to submitted. I don't know.