Why does the marriage institution exists?

I’ve seen a lot of people get divorced and sometimes I stop and start thinking if there is really a point in this whole marriage thing. The only thing there is is the divine bond. But why do people who marry by church have to marry legally? Are there any benefits. I see marriage more of as a contract to protect both parts. And probably for some good reasons, especially women. Still I dont understand why would a women that is not sure she is going to live with her husband for the rest of his life marry.