Why are celebrities invited to the Met Gala and the White House Correspondent's Dinner?

There are other people who contribute to art and have done more meaningful things that effect society and I just wonder why are celebrities invited to such events? The White House Correspondent's Dinner is to raise money for students who are interested in journalism so why invite celebrities who steal the spot light away from the main cause? It all seems like an ego booster to me. Do celebrities really know about art when invited to the Met Gala? Are they aware of the scholarships behind the dinner or is it just another "slap on the latest designer gown and make open mouth poses"? I understand if they contribute heavily towards the conservation of art or are strong advocates of journalistic scholarships that their invitation is warranted and deserved, but it seems like a "look at me!" type of event for them.