The DNC and RNC are organizations, there’s no reason outside of organizational preference for them to hold votes… They could flip a coin for all ‘voters rights’ are concerned. They are literally just fundraising organizations that pick someone to throw money behind.

Party affiliation, for all intents and purposes, shouldn’t even be listed on the ballots and the only reason they are is because the two parties realize splitting the country is a better way to raise funds than any amount of policy or good intentions.