I'm not married, though I've been with my partner for 21 years, we have one child together and I've just found out I'm pregnant with our second.
For me, marriage is a legal contract. It gives financial protection, means that the state recognises your partnership in a way it otherwise wouldn't, and it sets out the responsibilities of the couple to support each other. Like any other legal contract, it can be broken. It isn't any more or less special than any other legal contract.
Since having a child, we are now thinking of getting married/getting a civil partnership, purely so that our relationship is legally recognised if one of us were to die. We don't have a huge amount of assets but we own a house together and have some joint savings, and we also each have a small pension. I think being married would make things simpler if we died (neither of us are particularly legally/financially savvy, so getting legally married/partnered seems the easiest way to sort things).
I think historically it was steeped in patriarchy (being 'given away' by your father, for example, rape within marriage being legal, etc), but I think this is lessening as time goes on - at least in some cultures. I'm still more drawn to a civil partnership for this reason though; I can't separate marriage with the historical practice/application of it in my head, and the idea of being a 'wife' makes me feel uneasy.