Only because they have the money and fame to do it. Give your average voter plenty of cash and fame, and you will see some of the same stuff. You can certainly hear plenty of boneheaded stuff when they do "man on the street" interviews about political topics. Something like half or less of the US public even knows who the Vice President is. Only a few percent can name Supreme Court justices or the Speaker of the House.
I am frankly surprised by the fallacious arguments that are thrown around in the "study".
So, because your original argument fails, it is now ok to say "well, if this... then I would be right"? They do have money and fame, and that is part of what makes them who they are. Just because the average citizen we are comparing them with does not have money and fame, doesn't mean we can simply "presume" how they would behave if they did, and use that "presumption" in an attempt to strengthen our failed argument.
Perhaps in every thread in the study we should move forward with your faulty logic and say "well, IF black were white..." "well, IF straights were gay" "well, ONLY because Jews aren't Muslim" .... then I would be right and they would all act the same!
It's simply ridiculous. Such a presumption ignores all of the psychology, personality traits and sum of experience that's entices people into such Hollywood industries in the first place.
It's shocking too that you think the majority of average American citizens are as arrogant, self righteous and narcissistic as the "stars'.
Lastly, again you are confusing ignorance with arrogance and narcissism. Simply because many in America don't know who the VP is or who sits on the supreme court doesn't mean they are also arrogant and presumptions as are our Hollywood stars. Pull out a DSM and look up NPD... it's pretty common knowledge that the Hollywood elite manifest these traits at a far greater percentage than the average person.