To quote the Video Blogger host of "Shameful Sequels" in his review to "Garfield 2" (paraphrased): "Bill Murray refuses to do Ghostbusters 3 but he says yes to this shit?"
Apparently it was a case of mistaken identity:
Of course, this does not explain why he did the second one as well (but to be fair: he was the best thing about those films).
If you think that Cohen / Coen thing is anything more than Murray being completely tongue-in-cheek, you need to think again. Bill Murray is basically the ultimate troll, and with Garfield
, he got paid a truckload of money to go into a voice booth for a few days and record his dialogue.
In any event, I hope this finally kills the project once and for all.