In fairness to people who don't want a civil ceremony, the wording of the civil ceremony is a bit crap. I remember at my eldest brother's wedding it felt very odd, because the civil ceremony is so clearly modelled upon parts of the Anglican marriage ceremony with the stuff about G@d taken out. I don't think we really have a model of how to marry people in a non-religious way so the civil ceremony ends up being a pastiche of a Christian wedding.

Related to this, I think people are deeply confused about what marriage is and why you'd want to enter into it. If you're religious the answers are given by your religion, but why do non-religious people want to marry? My brother was very clear that he wanted to get married because he needed to marry his parter for her to be able to get a visa to go to Japan with him, but I don't think most people who get civilly married are quite so practical about their motivation.