People don't want to be left without faith because faith is hope and people want to have hope that something good will result from their deaths (i.e. eternal life) and that this life is not about nothing, but a preparation or expectation of the life to come, and a glorious one at that! It's soothing and comforting. But, there is no guarantee in hope, Reformed theology and Islam notwithstanding. That's why it's called hope. It's an expectation, not a guarantee.
So, fear is a strong element in faith and with fear people tend to hang on more tenaciously than with other things, which often leads to denial. And denial is not rational, so using reason is ineffective in changing one's mind.
It's much easier to make money selling hope without guarantee, as people flock to hope for comfort and security, even though it may be a false or non-existent security. People don't want to hear the negative. Negative doesn't sell. :) That's why politicians will never tell you the truth, but only make you feel hopeful that something will change (some people even get elected on selling such hope!). No politician will say "I will raise your taxes, because such is the reality" and expect people to vote for him.
So, when you sarcastically say I could make money on the issue of biblical prophesies not necessarily being fulfilled or true, I support your doubt and fully agree that such a thing will not sell but not because it is false.
Well, not since Mondale anyway. :)