When Do Memes Stop Being Funny?

Old meme is old. But why is this such a bad thing? Once the height of internetiness, the sight of a LOLCat now is unforgivable. Memes become passé crazy fast: after just months or even WEEKS of a new meme, we tire of the once hugely popular. Why does this happen, and happen so QUICKLY? Is it a reflection of the sheer volume of visual information we absorb from the internet? Or does it say something about this specific visual culture?