They annoy the hell out of me because people aren't even trying anymore to make them funny. Yesterday it felt like half of the memes were self-referential "haha it's so funny how we now post the old memes again" shit and people up voted them to the moon.
Sorry you didn't get the joke. They weren't referencing anything because they were only there to say "Hey, remember this one?" We all did, and the townspeople rejoiced.
If you don't get all warm and fuzzy for nostalgia, you aren't old enough yet.