Because there's atheists and religious people. Atheists use logic because they don't believe there's such a god controlling everyone, so they decide to use a logical answer to like: "Why's the sky blue?" or "Why are there days and nights?" while on the other hand, religious people think that God is the reality and logic at the same time. If you expected something different, it's because people have their own ways to see life and their own opinions, however, opinions aren't fact and they can be wrong... Hope this helped.

Principally because there are many things that cannot be explained by logic thinking like love, sexual attraction or greedy. No matter how intelligent a person might be, one has to admit there are a large number of people who are thinking with their gut feelings or sentiments much more than their logic thinking or the reality.