You actually think it’s too expensive to have a single followup vote to unify? You would rather let delegates be bribed by proxies of Soros and the Saudi prince who runs FoxNews?
I think that most times it doesn’t matter cause you don’t have someone running as a disruptor trying to highjack a party.
Ultimately, the party gets to decide who is their nominee. I’m not sure why this shouldn’t be the people who put the time and effort in, who support the party over the years and who would be expected to work hard to elect the guy in the general.
Voters get their input, but if they fail to coalesce I don’t see automatically deferring to a re-vote. Especially with states with open primaries.