Because it hasn't happened when it is predicted, over and over and over and over again, means that each time it has been intimated, it was a lie, used to sell books, raise money, or build a following.
Men lie ya know, even alleged religious leaders. Some deceive and others ARE deceived. Believe what you want. We need to live for right here, in the present, where God dwells with us, not in some imaginary and uncertain event for the future. While it is still called today, we need to live our lives. Planning for the future in practical terms is good stewardship. Get a job, raise your kids, love your family and friends, and face the FACT, unless there is a miracle that has not occured for 2000 years, we are ALL going to die, and most likely there will be no "magic curtain" for us, just as there has not been for the MILLIONS upon MILLIONS of beleivers who have gone on before us.
That is not a bad thing, it's a good one.
I have read all the books in the series and not once do they claim to know WHEN it will all happen. They don't give dates so you can't say that they are predicting any sort of day it will happen...