Dear Questioner,
You've unwittingly answered your own question, in part. Most porn is male made and male consumed - Therefore it is male-centric.
And males, are by and large, probably, bigger size queens and wang fetishists than women. We (the male public at large) want to have a large penis ourselves. It makes us feel powerful, captivating and yes, threatening. We want to pheel phallus power in all its mythological grandiosity. This, in part, means stretching a woman out with our huge manhood; this means seeing a woman struggle with us in her mouth; this means seeing a woman gape with wonderment and fear at our mega tool. Porn is fantasy. And in the world of fantasy we want to be Superman not The Penguin. We want to be dragons not dragonflies. We are willing to envision ourselves as the aged, fat and ugly Ron Jeremy because his penis is substantial and thus - all kosher.

There is porn out there that is more...pedestrian. The neighbors next door style porn. It can be found under the common heading, Amateur. And many porn users prefer it. There you will see men who aren't all carrying 10-inch flashlights, and women whose waists are ankle size. In porn like this the woman may actually appear to not be petrified or coked up. Here you will find, on the whole, men who pack various heat and women who can orgasm without sucking their own breasts to the point of mental illness.