People have been doing that for a surprisingly long time. I think it was encouraged by the fact that CoffeeScript is immediately intelligible to a lot of JavaScript coders, and authors reckon that anyone who has trouble can just compile it and get fairly idiomatic JavaScript.
I actually wrote a bookmarklet a while back that would look for CoffeeScript snippets on a page and translate them for people who find it troublesome, but didn't end up doing much with it because I didn't feel like there was much interest.