My gut feeling is that it has something to do with Arc. Some people tends to think it's just a regular Lisp with shorter keywords and that there's nothing really innovative in it. The problem is that pg kept the code private for too long while advocating publicly the power of the language and criticizing Common Lisp.

So when he finally released it, some lispers were disappointed because they've been waiting for something really disruptive. And it backfired as most of the time, the harshest critics comes from your disappointed sympathizers.

That being said, I don't hang that much on IRC so I have no real back-story supporting this.