I think the Mayans just didn't get around to making the next installment for their calander. "Hey Tlacolotl, are you gonna work on that calander or what?" "I thought I'd start it next year, besides our once great civilization is kaput so what's the point anyway, plus we've got, like, 500 years til this one's done so what's the rush? Hey who are all those bearded dudes getting out of those big ships?"