The simple answer is because he can and has proven in the past that he is more than capable of lying repeatedly and with a straight-face on more than one occasion.
Remember this?
This is the very same Dick Cheney who Bill-O says has to be believed. This is the same Dick Cheney that Dana Rohrbacher touts as the great truth-teller regarding the efficacy of torture. After all, how can we not trust the word of our venerable former Vice President (yellow cake?)?
Because Dick Cheney is a liar, has always been a liar, will lie about things he said on tape to reporters on national television and will keep on lying long after his lies are exposed as lies (weapons of mass destruction, anybody?).
Secretary Hillary Clinton had it right when she said he is not the most reputable source for information. Seriously, anyone with at least a second grade education should have figured out by now that if Dick Cheney's lips are moving it's a pretty sure bet he's lying. But that won't matter to all Cheney's fans on the right, especially his buddies at FOX whose motto is, don't forget, Fair and Balanced---of itself a real whopper of a lie.
So strap on your hip waders and fire up the sump pump as we revisit,for your viewing pleasure, some of the Honorable* Dick Cheney's finer moments!
(Truly Organic!)
Any of this ring a bell?