The question should be "Why can't McCain close the deal?" Here are the results of the last four GOP primaries.
Since Mike Huckabee withdrew following the Texas primary in March, McCain has secured enough delegates for the nomination, but has lost about a quarter of Republican primary voters in each of the subsequent four primaries. Here's a brief summary. First column is total votes in thousands; each candidate's column gives his percentage.
Votes (1000's) McCain Huckabee Paul Romney Keyes No Pref.
PA 4/22 790.0 73 11 16 -- -- --
NC 5/6 517.0 74 12 7 -- 3 4
IN 5/6 412.1 78 10 8 5 -- --
WV 5/13 100.8 76 10 5 ? ? ?
With 93% of the West Virginia precincts reporting, it looks very unlikely that McCain will break 80%. So far, I don't know where that remaining 9% is going since I can't find the official information.
Frank Rich was among the first to pick up on the deep mistrust of McCain, particularly among religious-right voters, with about 220,000 Pennsylvania Republicans going out of their way to make a statement. In Indiana, almost 20,000 voted for Mitt Romney. And in North Carolina, Huckabee and Alan Keyes combined for 76,000 votes, with Keyes picking up 13,000. Yes, Alan Keyes.
If this is representative of the schism in the Republican party, McCain is in big trouble. The Republicans are already in panic mode, especially after three straight special-election losses of House seats. And once McCain loses and the party loses ground in Congress, the subsequent civil war will make the current Democratic tiff look like a Sunday-school picnic. I can't wait.