Here you have the biggest state, but one party is so clearly going to win that it makes no sense for a presidential candidate to cater to it. Nor should either party pick its nominee based on what Californians will like. Isn't that bad for California? But since the majority is Democratic in California, and the Democratic candidate currently has a lock on all 55 electoral votes, why should that Democratic majority vote for a change that will only cede some of those votes to the Republican candidate? The proposal looks doomed.
But wait. Even if most voters who vote Democratic care mainly about the party's dominance at the national level, all you need is for some of the voters who vote Democratic to care more about the candidates' paying attention to California. Add those votes to those of the Republican minority, and you could get to a majority for change.
The strongest reason for having a winner-take-all approach in any given state is that it makes winning that state highly valuable and induces the candidates to fight hard over those few voters in the middle who have the power to throw the whole pile of electoral votes one way or the other. But if the balance in the state isn't close enough, the candidates won't fight over it, even if the number of votes is high. That's California.
And here we see why you're never going to get all the states to change together. The winner-take-all approach makes sense for some of the states. Awarding the electoral votes proportionally would make some states very unimportant and would undercut the huge power currently enjoyed by a few big states like Ohio and Florida.
ADDED: No sooner do I post this than I see "Giuliani says he can carry California."
“I'm the only Republican candidate that can carry on a campaign in every single state, and we can be competitive in every single state"...Well, perhaps I like California in its winner-take-all position. It may moderate the Republican Party. And the Democratic lock on the state has not always been there. Maybe things really aren't that dysfunctional -- at least from the perspective of someone who likes Giuliani. Which might mean that more Democrats now ought to shift over to wanting the change.
“If one of the others is nominated, there'll be no campaign in California. California will be conceded to the Democrats as it has been since Ronald Reagan.” (Former President George H.W. Bush did in fact carry California in 1988.)