I do not have a ready-made explanation for this curious fact. This may be due to the lexical and structural complexity of the PNAC's documents. Another possible explanation is that PNAC was never directly mentioned,- approvingly or disapprovingly,- in any of the two major parties' campaign speeches that I am aware of, and the major media sources were never thorough enough to "discover" and research it on their own.
Be that as it may, let me present Bernard Weiner's execellent introduction to PNAC. I think Weiner has done a really good job of describing both the history and the ideas of PNAC.
In the early-1990s, there was a group of ideologues and power-politicians on the fringe of the Republican Party's far-right. The members of this group in 1997 would found The Project for the New American Century (PNAC). Their aim was to prepare for the day when the Republicans regained control of the White House -- and, it was hoped, the other two branches of government as well -- so that their vision of how the U.S. should move in the world would be in place and ready to go, straight off-the-shelf into official policy.
This PNAC group was led by such heavy hitters as Donald Rumsfeld, Dick Cheney, James Woolsey, Paul Wolfowitz, Richard Perle, Bill Kristol, James Bolton, Zalmay M. Khalilzad, William Bennett, Dan Quayle, Jeb Bush, most of whom were movers-and-shakers in previous Administrations, then in power-exile, as it were, while Clinton was in the White House. But even given their reputations and clout, the views of this group were regarded as too extreme to be taken seriously by the mainstream conservatives that controlled the Republican Party.
Weiner provides a point-by-point list of objectives the PNAC authors envision America fulfilling. He summarizes them thusly:
Chief among them are: 1) the policy of "pre-emptive" war -- i.e., whenever the U.S. thinks a country may be amassing too much power and/or could provide some sort of competition in the "benevolent hegemony" region, it can be attacked, without provocation. (A later corollary would rethink the country's atomic policy: nuclear weapons would no longer be considered defensive, but could be used offensively in support of political/economic ends; so-called "mini-nukes" could be employed in these regional wars.) 2) international treaties and opinion will be ignored whenever they are not seen to serve U.S. imperial goals. 3) The new policies "will require bases and stations within and beyond Western Europe and Northeast Asia." In short, the Bush Administration seems to see the U.S., admiringly, as a New Rome, an empire with its foreign legions (and threat of "shock&awe" attacks, including with nuclear weapons) keeping the outlying colonies, and potential competitors, in line. Those who aren't fully in accord with these goals better get out of the way; "you're either with us or against us."
I can not claim to have read all of the PNAC's documents and they are quite numerous and at times quite cryptic; however, those I did get through are pretty much consistent with Weiner's description above. I think his article is a must-read for anyone seeking the truth about what people in charge of the US policy today really think.