A superb observation from the footnotes of Adrian Tchaikovsky:

(1) Leaving aside the New Age types who have rather galloped ahead of the pack in declaring the end of the world, scholarly debate suggests there is no actual evidence that the Mayan calendar portends anything apocalyptic at all (from the wretchedly sparse material available). It seems just as likely that they were all marking their great great… grandchildrens’ diaries for a particularly good party (2)

(2) Which in turn suggests that the Mayan culture was built on absurdly extended forward thinking and a careful attention to scheduling, and possibly the Spanish dealt them such a blow just because they failed to call ahead and book their invasion.