Tony Lee writes a good piece but leaves out a sixth reason, one I can't believe he didn't mention:
6. The Evangelical vote in Arizona is small. This hurts Santorum who's a two-trick pony--abortion and homosexual marriage, the two issues most important to Evangelical voters. Arizona is a law-and-order state. Conservatives there are mostly concerned about crime/illegal immigration which are NOT Santorum's strong points. If you look at the states that Santorum has won--Iowa, Minnesota, Missouri and Colorado--it was the Evangelical voters who gave him those victories. And in Missouri, he had the added benefit of Rush Limbaugh telling Missouri's Gingrich supporters to vote for Santorum as Gingrich failed to get onto the Missouri ballot.
Lee also doesn't mention the fact that Michigan (whose primary is tomorrow as well) like Arizona has a small Evangelical population.
My thanks to americanpatrol.com for posting this.