I'm amazed at how many musicians and celebrities do voices or cameos

When I first watched an episode of Mr. Pickles, I hated it, but after I saw a few more it grew on me (basically the way I felt about Tom Goes to the Mayor). Since Mr. Pickles appeals to a fairly small percentage of viewers and isn't well known, I'm curious how they managed to get so many musicians and celebrities to voice characters on the show: Brooke Shields voices Mrs. Goodman and cameos are made by Iggy Pop, Rob Zombie, John Waters, "Weird Al" Yankovic and others.I thought it was especially strange that Iggy Pop did a cameo on Mr Pickles when he could have played himself on [adult swim]'s BEST show, The Venture Bros.!

It's also kind of strange that the show's theme song sounds exactly like Nathan Explosion and Dethklok but apparently Tommy Blacha and Brendon Small weren't pissed about that?