theprestige
Penultimate Amazing
While the party might be picking the candidate as you say, the primaries are a good way for specific issues to gain support and acknowledgement. Even if the choice of person is predetermined, the end package of policies they are bringing will be influenced.
Hm. That raises an interesting question about the Hillary Clinton campaign.
Sanders claimed that he entered the primaries not to compete for the nomination, but to make sure certain issues got supported and acknowledged. I'm wondering if that perception, that Clinton had onboarded some of Sanders' issues, siphoned off some swing votes in the general election. Perhaps Clinton might have won if moderates hadn't been reminded that she also represents the Sanders wing of American politics.