There are often major rifts within parties. Party platforms seem to be diminishing, are more of a formality, and are not always followed by winning candidates when they take office. Voters may like some positions of two or more parties or not like some positions of any party. Many voters don't affiliate with any party. Voters often vote against candidates they don't like rather than for candidates they like. I don't know how many voters look primarily at a candidate's party affiliation when choosing who to vote for or how those voters might adjust to not knowing a candidate's party affiliation.
Party primaries or caucuses are not needed to choose a winner. Ranked Choice Voting could allow a single election to determine a majority winner in a single election regardless of how many candidates are running or how many candidates have similar positions. Voters could vote for the candidate they most want without fear of unintended consequences such as a "spoiler" or "long shot" candidate giving the election to a less favored candidate. I'm new here and not yet allowed to post links, but if you're not familiar with Ranked Choice Voting, a search will show many websites with details, examples, and videos. As with any internet search, information quality varies.
There's more ideological cohesion now between the two major parties than there basically ever has been before though. I agree on RCV for sure though
