Kurzweil since 1982 is easy to understand.
His predictions are part of his personal eschatology. He is man in religious quest for personal salvation.
All his past predictions and timeframes are conveniently set so that there is change for him to live forever. He is nutrition and immortality nut (Fantastic Voyage: Live Long Enough to Live Forever and Transcend: Nine Steps to Living Well Forever). He is now 72 years old. If he lives to old age with all his life extension pills and rapture of the nerds happens in 25 years he could just make it.