This seems like a good place for my current theory on Deity.
Deity is big, very fucking big...it's all around us, and in us. It's the life force that holds everything in the entire universe together...humans, aliens, trees, rocks, animals...the whole shabang. It's so bloody big that it is completely unfathomable to us. But being the curious creatures that we are, we want to understand, so we search. And being the (relatively) small creatures that we are, we need to bring this Deity down to something that we can understand and get a grasp on to even begin to understand.
So...we tend to worship in the form that we are used to, or more comfortable with. Christianity's male God figure is currently popular in a male-dominated society. Early feminists (the suffragettes) rewrote the bible (Elizabeth Cady Stanton) and started talking about the feminine aspects of God. Modern feminists talk about the Goddess predominantly.
I can't speak to other pagans, who haven't been as influenced by feminism (although few of us today are not influenced by the changes the suffragettes caused to happen)....perhaps it's family tradition passed through the centuries, or a kind of genetic memory. I'm sure there's oodles of explanations that would work.
The point is that Deity is completely beyond our fathomability...I'm not even sure it's sentient in quite the same way we are.
I worship Deity as Goddess because of my feminist background, and my pride in, and love of, being a woman. But I never forget that "Goddess" is just a convenient shorthand for something I will never understand and keep trying to...