Because they are really good at it
You can't make a paper aeroplane out of an elephant!
The leaf, the Emo is too depressed to go outside. I saw this joke reposted so many times. I figured I'd mix it up a bit.
Ruff Bark
Hide and go zika
Want to hear a clean joke? Bob took a bath. With Bubbles. Want to hear a dirty joke? (Punchline hidden so you don't accidentally read)