> Yet every year we have just a handful of candidates

You must have very large hands, unless you are only talking about major party nominees (i.e., winners of the first round of voting from the two biggest parties.) There's a reasonable basis, arguably at least, for limiting consideration to major party candidates, but the nomination process is part of the selection process and the candidates that enter that process, not just the ones that win it, are part of the choice set. If one ignores the process until after most of the critical decisions are made, the remaining choices are quite limited, but that is itself a choice.