In the NFL between 1990 and 2011 there were 23,684 PATs attempted. Of those just 103 were blocked and 256 were missed straight out.
If you are willing to accept these numbers as near-accurate even at the college level the likelihood of blocking the PAT is less than 0.5%. The likelihood of marching the field and getting points to win the game in just 45 seconds isn't crazy high either, but the way the game was going it was without question better than 0.5%.
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No reason translates roughly to "no good enough reason".