Because it's funny. Even if it is kind of dark and a little mean. I actually love snails and would never pour salt on one, which kind of makes this even funnier to me in some weird way...
(originally drawn around 2009, but edited more recently)

Products with this design (and with a "bleeped" version on this design) are available on my Redbubble: redbubble.com/people/kyttibat