The answer to this would seem to be that ancient monotheistic societies perceived males, both animal and human, as being stronger than females. It was therefore natural for them to describe God in a male rather than a female way.
Angels in Judaism, Christianity, and Islam are also always male (even if some artists make them look feminine!) probably for the same reasons.
Polytheistic religions have a different approach and male deities have female counterparts or consorts (for example: Brahma and Saraswati, Vishnu and Lakshmi, Shiva and Parvati, in Hinduism). However, Brahman the Hindu Supreme Spirit of the Universe, has no gender.
Today many religious people see God as being beyond gender. Others have sought to make a point by describing God as female (see feminist theology).