The party can be about backroom bargaining or follow the voice of the voters.
The problem is that the "voice of the voters" is not clear. It's clear if one candidate wins a majority of delegates before, but it's not clear when you have a situation where no candidate has a majority. This happens all the time in multi-party democracies where there are lots of parties. The party that wins the plurality may be the most disliked party in the election, and the other parties all unite against them because a majority of voters don't like the party that one the plurality.
So five votes short is not clear but one vote over is? OK..keep playing the GOPe rules and enjoy years of one party rule because the Republican party will be dead.