In #California, some years back, they passed a law to restrict general elections to the top two vote-getters in the primaries, so that no third parties ever get the chance to get before the main electorate.

That affects me as a "decline to state" a party voter, because there's zero chance for me to vote for someone whose views and agenda are similar to mine. (Not that I've seen any third party candidates whose views are similar to mine, but if such a candidate ever arose, they aren't likely to be in the Democratic or Republican parties.)