There are many reasons why lots of otherwise reasonable people don't 'believe' in the theory of evolution. Yes, some of it has to do with their religious background and with a lack of basic education concerning science generally and evolution specifically, but that can't be the whole story.Part of it also has to do with the way our minds work. For instance, we have a natural tendency to think teleologically (in terms of goals, purposes and design) and in terms of agency (there must be some intentional mind or subject behind any given phenomenon), and so we commit a basic category mistake when we apply these modes of thinking (the manufacture of industrial and commercial goods) to non-teleological phenomena (like biological complexity and organic processes).
But it doesn't stop there. The problem is that as evolved creatures, we have inherited a set of cognitive quirks and biases that conferred our ancestors with practical benefits that are not always conducive to the attainment of truth. To add insult to injury, our cognitive biases often lead us to commit logical fallacies, like the God of the Gaps argument.
In the following fascinating and amusing presentation, Neil deGrasse Tyson explains how even some of the greatest scientific minds of all time, people whose education and intelligence are unimpeachable, when confronted with the limits of their own knowledge and understanding, quickly retreat to this pernicious mode of poor thinking. In the process, he draws some deliciously thought-provoking lessons.