Why is it that some of our senses win out against others?
Why is it that our eyes have such a hard time believing what our ears hear?
Why is it that we can hear our Lord’s Words, “Take, eat; this is My body” and “Drink of it, all of you, for this is My blood of the new testament, which is poured out for many for the forgiveness of sins,” while we simultaneously convince ourselves that we are only seeing bread and wine?
Why does sight win?
Why is that?
letitstet.com 
People don’t believe because that because they’re stupid, sinful, and they would rather have the assurance that they can get themselves out of their own mess.
Sorry, I guess that question was rhetorical, but you did ask it.