Because we've had six long seasons of Democratic rule. It's time for a change. Jed Bartlett was a great man, but Matthew Santos is no Jed Bartlett. Bartlett was a smart, even handed president who hired such notable Republicans to serve under him as Ainsley Hayes and Joe Quincey. Would Matt Santos be so bold?
Vinick, on the other hand is a True Republican Moderate, a centrist who believes that the governments role should be limited and personal freedom should be the rule of law. He's given the finger to Big Tent politics running rampant in the party and is easily the most electable president the Bartlettverse has seen in decades.