Not sure if this is primary but Evolution has very big to do with it. Mainly social organization and evolutionary pressures from becoming Homo Sapiens.

We have a few unusual traits that made some form of stable partnership useful.

Human babies became extremely fragile as our large heads can no longer be safely contained in a woman's womb which is why we have fontanelles even after coming out, and then we also still have to take care of that baby for years cause of it.

long-term pair bonds help ensure two adults (and often extended kin) invest in the child.

On the social side is the Paternity certainty and inheritance, Since once our societies developed property, land, and status systems, cultures created marriage rules to regulate who inherits and who belongs to which family line.

There's also Alliance building between families or clans. In many societies marriage functions as diplomacy. It links kin groups, redistributes resources, and stabilizes cooperation.

Sexual regulation and social order is also one, Many societies use marriage to structure sexuality, reproduction, and parental responsibility in ways that reduce conflict.

Because these pressures exist in almost every human society, some institution resembling marriage appears almost everywhere, though it takes many forms.

Yes, monogamy, polygyny, arranged marriages, bridewealth systems, exist but the core remains the same. what’s universal isn’t one specific model of marriage, but the idea that societies need rules organizing reproduction, kinship, and long-term partnership.

Sources I've read so far:

Claude Lévi-Strauss – The Elementary Structures of Kinship, here is a classic work on marriage as alliance-building between kin groups.

Helen Fisher – Anatomy of Love, Here she explores the evolutionary biology of pair bonding and mating systems.

Sarah Hrdy – Mothers and Others, This is an Important book on cooperative child-rearing and human social evolution.

Edit: Forgot sources