Think of it this way - imagine nationally the election is close and how your state distributes EC votes determines the outcome. Let’s further say 70% of your citizens voted for candidate A, but for candidate A to win nationally they need all your EC votes. Given that your state laws should primarily be for the benefit of said state’s citizens, would you really want an outcome that 70% of your state’s voters don’t want? All it would take is one election where this determined the outcome before the voters would make it “winner takes all”.