Because some memes become entrenched? Even when they're hopelessly outdated and require lots of filtering or creative interpretation.

Relevant as in for the current topic.

Not relevant as in influence. Bugs influence me too, but its not relevant most of the time.

“All flesh is like grass and all its glory like the flower of grass. The grass withers, and the flower falls” — 1 Peter 1:24

“Like a tiny drop of dew, or a bubble floating in a stream; Like a flash of lightning in a summer cloud, Or a flickering lamp, an illusion, a phantom, or a dream.

So is all conditioned existence to be seen.” —Diamond Sutra