It has more to do with the arcane rules surrounding delegates, which are different between the parties. In the event Trump wins enough delegates to secure the nomination but is unable to accept due to an untimely event, Haley may be in the best position to take advantage of that if she is the only other candidate with delegates of her own. Most Republican primaries are winner-take- all, so Haley winning even a single State is significant. (By contrast, if Democrats worked by the same rules, then the “uncommitted” vote would not have earned any delegates.)

The entire Primary process puts a thin veneer of Democracy over what is very much an internal party process to select a candidate.