It's simply the most comfortable way to suck cock, isn't it? Kneeling before a standing man. Nothing to do with prayer, supplication, submission; it puts my mouth at cock height and his cock at mouth angle and that's all it means.
But the truth is sometimes it is about submission, about kneeling while he stands, about his hand on the back of my head and his hips thrusting forward faster and further than I would dare let him if I had control.
And sometimes it's not. Sometimes it's about seeing him go weak in the knees and nearly lose his balance and be forced to make me stop even though he doesn't want me to stop.
And sometimes it's just about not having to walk all the way to the bed or the sofa when he's just greeted me at the door and I want to do it now.
The one thing it's never about is him and not me. It may only be his genitals but it's both of our bodies. I'm acutely aware of his taste, his shape, every tiny reaction of his body, and I fucking love it.
A blowjob isn't a gift. It's sex.