Because of the Sheer Number of Joseph Smith”‘s False Prophecies:
False prophecy became a habit for Joseph Smith. Most estimates of the number of recorded false prophecies that Smith made range from 50 to 60. Edmond C. Gruss and Lane A. Thuet in What Every Mormon (and Non-Mormon) Should Know have documented the fact that Smith made at least one false prophecy per year from 1829 until the year of his death.
Wow.
For more information, see The Mormon Mirage 3rd Edition: A Former Member Looks at the Mormon Church Today (Zondervan, 2009). Also available as an audiobook and as an expanded-text E-book for Nook, Kindle and other reading devices.
