Faith was an important aspect of society in a time when little was understood about science because it outlined a purpose for the existence of everything. As our understanding of science grows, however, faith plays a less and less significant role in our lives. Those who hold onto faith above science tend to be individuals who are not well educated and are somewhat ignorant of many scientific principles either because they choose to be or are persuaded to be by those who are much more manipulative than themselves.
In a lot of cases, people believe in God because of that, but in a lot of other cases, it's simply because they genuinely believe in such a superior being. In other, very common cases, people believe in God because they value tradition and their beliefs are part of their traditions.