Why are most celebrities Democrats

While everyone knows Hollywood stars and in general, most celebrities are Democrats, does anyone know why?
This might shed some light on the subject when you compare the Celebrities that are Democrats and the Celebrities that are Republicans.
These Celebrities are Democrats:
Woopie Goldberg
(High School Drop-Out)
Christina Aguilera
(High School Drop-Out)
Christina Applegate
(High School Drop-Out)
Kevin Bacon
(High School Drop-Out)
Roseanne Barr
(High School Drop-Out)
Mary J. Blige
(High School Drop-Out)
Pierce Brosnan
(High School Drop-Out)
Jim Carrey
(High School Drop-Out)
Cher
(High School Drop-Out)
Elvis Costello
(High School Drop-Out)
Russell Crowe
(High School Drop-Out)
Robert De Niro
(High School Drop-Out)
Johnny Depp
(High School Drop-Out)
Rupert Everett
(High School Drop-Out)
Natalie Imbruglia
(High School Drop-Out)
Iman
(High School Drop-Out)
Catherine Zeta-Jones
(High School Drop-Out)
Jude Law
(High School Drop-Out)
Jennifer Jason Leigh
(High School Drop-Out)
Courtney Love
(High School Drop-Out)
Demi Moore
(High School Drop-Out)
Mackenzie Phillips
(High School Drop-Out)
Joaquin Phoenix
(High School Drop-Out)
Keanu Reeves
(High School Drop-Out)
Charlie Sheen
(High School Drop-Out)
Uma Thurman
(High School Drop-Out)
John Travolta
(High School Drop-Out)
Steven Tyler
(High School Drop-Out)
Estella Warren
(High School Drop-Out)
Neil Young
(High School Drop-Out)

Here are some Celebrities that are Republicans:
Robert Davi
(Graduated from Hofstra University)
Jim Caviezel
(Graduated from the University of Washington)
Dean Cain
(Graduated from Princeton)
Brooke Shields
(Graduated from Princeton)
James Caan
(Graduated from Hofstra University)
Julie Bowen
(Graduated from Brown University)
Tom Selleck
(Graduated from U.S.C.)
Jeff Foxworthy
(Graduated from Georgia Tech)
Andy Garcia
(Graduated from Florida International University)
The Rock Johnson
(Graduated from University of Miami)
Dennis Miller
(Graduated from Point Park University)
Craig T. Nelson
(Graduated from Central Washington University)
Writer Tom Clancy
(Graduated from Loyola College)
Jerry Bruckheimer
(Graduated from Arizona)
James Woods
(Studied for three years at M.I.T.(!) )
Jon Voight
(Graduated from Catholic University of D.C.)
Rip Torn
(Graduated Texas A&M;)
Sylvester Stallone
(Graduated from Miami Dade College)
Kevin Sorbo
(Graduated from University of Minnesota)
Robert Duvall
(Graduated from Principia College)
Patricia Heaton
(B.A. The Ohio State University)
Sela Ward
(Graduated from the University of Alabama)
Ron Silver
(Graduated from St. Johns with a Masters Degree)