Reason #1: Calendar shift.
Currently, I'm encountering people freaking out because oh my god 21st December 2012.
You do realize, of course, that the Gregorian calendar is a fairly modern innovation- one of which the Egyptians and Mayans were completely naive?
Also, you do realize that the transition to the Gregorian calendar, back in the 1700s in Britain, though as early as 1585 elsewhere, divorces all previous predictions of dates from calendrical significance?
Reason #2: Bitch please.
Every person who has thus far predicted that The World Will End On Insertdatehere has been proven wrong. Using Occam's Razor (that is: the simplest thesis is the one most likely to be true), it holds most probable that people who predict the world will end on a date in the future will be as wrong as people who have predicted the world would end on a date that has passed.
The current cycle of the Mayan calendar ends in 2012. Note- 'current cycle'. Not 'calendar'. It also ends in December of 2012.
But does it end on the 21st of December? Nope. It ends on the 23rd. OR the 21st. Or the 23rd. Or. Note the indecisiveness, there? Yeah.
Does it mean 'the world will end'? Nope, it means that the current cycle ends, much as we experienced on Jan 1, 2001, with the end of the prior millennium.
Reason #4: Oh like you're so important.
The universe, in main? is an unreasoning bit of clockwork. There's a bunch of quantum bullshit going on under that which is totally not clockwork and is kind of brainmeat-hurty, but let's ignore that for the nonce and go with Newton's model- which is smarter than most millenarian anyways. The universe doesn't give a tinker's damn about what us tiny little humans are doing on our slightly less tiny little planet, with our picayune little lives.
The universe has bigger concerns than ending life on Earth in 2012.
reason #5: Grow a goddamned vocabulary.
No, there isn't any coded wisdom in Mayan codexes that suggests the world will be destroyed by X in December of 2012. It's just the end of one reallyfuckingbig span of time and the beginning of another one. BTW, the Maya named this reallyfuckingbig span of time a baktun. it's about 394.25 years long. Specifically, 144,000 days long. That's all it is. It's not the end of the universe, it's not the beginning of the universe. The classical period of Mayan civilization occured in the 8th and 9th baktun. Did they 'plot out' what the span of the 13th baktun would look like? no- because the Mayans were astronomers, not prophecy-makers.
BTW: you just read the term 'baktun' for the first time, didn't you? Thought so.