Maybe it is a political thing. It attempts to give celebrities some validity and makes them look knowledgeable so when they give an opinion it seems more credible. I agree with Brad Pit after he did the movie about Tibet:
Originally Posted by Rob Keeble
"You shouldn't speak until you know what you're talking about. That's why I get uncomfortable with interviews. Reporters ask me what I feel China should do about Tibet. Who cares what I think China should do? I'm an actor! They hand me a script. I act. I'm here for entertainment. Basically, when you whittle everything away, I'm a grown man who puts on makeup."
— Brad Pitt
I love the movies Brad is in but I take his advice when he talks about anything else.
They might think it makes it more appealing to the viewer to have celebrities do cameos.
Asking an actor for information or opinions like asking an the weather man about brain surgery just because he has a degree. The actor doesn't necessarily have a degree.
It wasn't a party unless it involved fire, an ATV, a chain saw and whiskey.