If you look at the various forms of God,(God is formless, but we humans, give HIM a form for various reasons(which can be a topic by itself btw!)) various philosophies have been represented in different ways.
For example, hmmm, Sri Aanjenayar depicting the control of the "monkey"-like mind, dissolving negative thoughts and keeping the mind intune with God AND the snake held at the legs of Lord Murugan's vahanam, the peacock, also represents the control of the human mind, doing away of any negative thoughts.
Different representations to represent philosophies in different ways..
And according to our culture, tradition and even in Hindu Philosophy, females are highly respected and at times are given the kind of respect God gets.
Amman is also known as "Sakthi(Power)"
This could link up to why females are used to represent Sakthi.
Further to this, I`m sure they have other good reasons for this representation as well.
And it is also probably our Human mind which always links a female figure beside anyone as the wife?!
Our Puranams, do depict Gods being married and all. But once again, we have to explore what a puranam actually is. Hindu philosophies and sciences, can become complex and not all can understand and appreciate it easily.
Simply put, Puranams are "Hindu philosophies that are made into a story-like form by Great Rishis/Siddhars.." so that it reaches a wider range of people, from scholars to the illiterate men and women as well as kids.
You can't go to a kid and explain to him Dharma/Karma and all. But if you tell it in a story-like form, the message gets across very much easily.