STV winner-takes-all could fix some of the problems of a candidate with a minority and narrow plurality winning all the votes. It would mean that if a few candidates with very similar ideologies were running against a single candidate on a different platform, while the few similar candidates would initially split the vote, after the distribution of preferences it is more likely that one of them would end up receiving the delegates. It would still allow the party to choose a candidate quickly.
Americans don't like STV because it's "too confusing". But Republicans generally, as a party, have some sort of moral opposition to proportional representation. (Not that some don't support it, or some Democrats oppose it, but PR certainly has more support among Democrats than Republicans, where it has support at all.)
