There are many reason "why" we believe in God. I couldn't possibly give you all of them. Some were raised to believe in Him and have never questioned it. Some people have been at a very critical point in their life where only a 'miracle" can explain the outcome. Others believe in someone more powerful, more insightful and omnipresent to explain such things as creation and the "un-explainable".
Note: Not believing in God, doesn't mean He's not real.
Note: Not believing in God, doesn't mean He's not real.