The two major parties are geographic coalitions rather than representatives of particular groups or views. Major party candidates *cannot* say, "I’m running for President. Here’s what I stand for. If you don’t like it, don’t vote for me," because their members don't stand for any single thing. The candidates must speak as leaders of coalitions in order to win. Electoral reform (instant runoff or cumulative ballot) might change this, but for the moment, no national major-party candidate can say that and win.
I've come to believe the whole ambiguity thing is really weird; the parties are coalitions, they can be understood as such, and one can, sensibly, pick which one prefers. I am unhappy that our national political discourse does not allow for coalition forming outside of the two major parties, but that's no reason to prefer King Stork to King Log. Or not to vote against King Stork.