The reason is that it is translated from the Hebrew. Hebrew has no neutral gender nouns (such as it), any noun is either male or female, even if there is nothing male or female in them. For example, a chair is male, but a couch is female - that is grammatically in Hebrew, as they don't really have a gender. The default in Hebrew is that a noun is male. So the noun God, even though God has no gender per se, is treated in Hebrew as a male noun, just like a chair. Since Hebrew uses "He" to refer to God as God is male from a grammatical point of view (Hebrew also refers to a chair as "he" for the same reason - there is no "it" in Hebrew), the Bible says "He", and translations to other languages just went literally.
Since male and female are created in God's image, I believe God is neither sex but a spirit. Obviously Jesus was man, the Son of God. Many modern day churches are getting away from referring to God as he. For example they don't want to say Father so they say Creator. Even though I believe like I do, it's still easier and less awkward to use "He" in the traditional way.
Well first off, I'm a Christian and I don't believe God is a male, he has no gender but some of the reasons why we refer to Him in the masculine term is because his son called him father repeatedly in the New Testament and he made man in his image then made woman for the man (it doesn't say woman is made in the image of God but that doesn't mean women are any less important according to the bible as many people think) and finally because God, Jesus, and Holy Spirit are all one in the same and we know Jesus was a man and not a woman, but really, God doesn't need a gender like we do so it is kinda confusing but most of his names mentioned in the Old Testament are masculine as well (ex. King of kings not queen of queens)
Because the Hebrew and Greek both have definite feminine articles, and they are never used of the Almighty. Not once. God has no gender as Lior rightly states, but He always calls himself by the masculine pronoun. Now, if a transgender person wants to call himself a she, you abide by it, right? so why would you challenge the self-speech of God?
God is Spirit, not male or female. The Bible clearly refers to God as male in its original languages, and Jesus referred to God as Father. Christians follow the biblical pattern. Doing so affirms what God has said and His role as our heavenly Father. God chose to be revealed in this form in order for man to more easily grasp who He is.
The world is, even now, a male dominated place. God did create the male first and gave to him dominion over ALL things. Woman was created second FROM part if Adam. Adam, the male, was given leadership. Until midern days pretty much every society was male centered. Women had few if any rights. Biblical days were this way. Christ was born a male because no one would have listened to a woman. Has God made Jesus female and tried to do even a small bit of what Jesus she almost certainly would have been stoned to death or imprisoned within the first month. Jesus had to be male so people would listen. God is a genderless spirit being but we have to refere to Him somehow and saying 'It' diesnt sound right and having to write and say 'He/She' and 'Him/Her' all the time would be too difficult. God gave dominion to the male. Refering to God as 'Him' is tradition and its easier.