The meme that the world will end in December 2012 comes from two sources:
1. Humans like predictions, especially predictions of the end of the world -- maybe because they're not happy with the world as it is (and maybe for good reason), and a prediction of the end of the world is part of the (still widespread) Christian worldview.
2. The "2012 Phenomenon" has, since the start of 2012, got a lot of attention. This is the widespread expectation of something Big happening in 2012 (a desperately-needed social/cultural transformation?). The roots of this are in the writings of Jose Arguelles on the Maya Calendar and in the talks and books of Terence McKenna, whose Timewave Zero theory posits an 'end of time' at which point novelty/complexity in the universe goes off the scale. This 'end point' is generally believed to occur on December 21, 2012. But what is generally overlooked is that, although McKenna mentioned this date often, it is not strictly implied by the theory of TWZ -- it was an estimate that McKenna made sometime in the 1980s, and his estimate may have been flawed. So TWZ does not
assert that time or the world will end in 2012. For more on TWZ see Terence McKenna's Timewave Zero Theory