Because of people like this.
Let's identify the behaviours displayed:
* Smug ("He knows what's right.")
* Self-righteous and intolerant of other views ("It should be make-or-break for everybody.")
* Denying facts ("That isn't Christianity...")
* Plainly self-destructive - she is voting against her husband's interests as a worker
* Blindly foolish ("The Lord will provide.")
There are others, but I've run out of buckets to vomit into.
Yes, I personally believe this woman's faith to be misplaced. I'm not trying to make any points about that one way or another here. Most people would agree, even in principle, that it's best to do what you can to help yourself before relying upon anything or anyone else - "the Lord helps those who help themselves", even if you take away the L-word. This woman is just stupid, no matter what you believe.