It admittedly gets game-theoretically a bit less than straightforwardly-good to unilaterally open up one's state's races to more parties when that probably mean

It admittedly gets game-theoretically a bit less than straightforwardly-good to unilaterally open up one's state's races to more parties when that probably means weakened political influence, in an environment where the vast majority of races are still FPTP and the two-party system will dominate. Plus both of those two parties' leadership-class agree it's a bad idea, because it would weaken their parties and their personal power, so will tend to propagandize against such measures.