A smart candidate will strive to make the tent more inclusive in the general election, to collect their supporters.
Paul's attractive qualities (Strict Constitutionalist/ Fiscal Conservative) are blown to hell and gone by his unattractive attributes ("It's America's fault"/ Appeasement). To bring Dr. Paul into the tent alienates at least 90% of the party.
That's one of the things about Paul supporters I don't understand. Some truly believe that their 6 or so percent should dictate the party direction. Whether you are "right" or not is irrelevent. We are a Constitutional Republic. If you can't generate votes, you get to lose.
To believe that the (vast) majority should cater to your views can only strike someone watching from the outside as naive and adolescent.
I think some are starting to realize (finally) that "he can't win" really is a valid indictment of Paul. Some of us hoped he could serve to move the Party back to the right, but unfortunately, he's failed to exhibit the leadership neccessary to keep some of his more...um...undesirable supporters in check. All he's done is alienated the base. That's unfortunate, but true.