Because Gallup is a good pollster and the others are biased, poll on weekends, use bad methodology, etc., etc. ;)
"Because Gallup is a good pollster and the others are biased, poll on weekends, use bad methodology, etc., etc. ;)"
Thirty years ago the big three pollsters were Lou Harris, George Gallup and Bob Teeter(Market Opinion Research)
Today anyone with a computer gets into the game.