John Major Jenkins has looked into the question of why the Maya ended their 13-baktun cycle in the Gregorian year 2012, and has researched the matter in incredible detail, and comes to conclusions that result from detailed study of many archaeological and specialist works. His study shows that the Maya deliberately targetted this point in time as the end of the cycle, and the evidence is found in king-accession rites, mythology, architecture, and the ball-game.
As you will know if you've read other reviews, the reason is the alignment of the winter solstice sun with the galactic equator - an event that happens only once in a cycle of precession - around 26,000 years. This IS NOT the "alignment of the solar system with galactic centre" or any of the other misrepresentatations of his work that have appeared.
This work stands whether or not anything noticeable happens in the years around 2012 - the fact is, that the Maya predicted that something would happen around 2012. This has become evident since the publication of this book, since the Tortuguero prophecy entered the public domain. In April 2005, the existence of Tortuguro monument 6 was revealed, (though known to a few specialists before that). The stela gives the end-date 4 Ahau, 3 Kankin, 13 Baktun (a combination of 3 calendars that gives the 21 December 2012 date) and gives an accompanying prophecy of the return of the Nine Gods.