What an odd collection of things to say.
Why does it matter so much? Marriage, to me, is a formal commitment to a sharing of lives. It also has some good tax benefits. For others it is a reflection of their faith and their values, their community, their commitment, their need for belonging or security, a union, the creation of a family, a sense of belonging or identity etc etc. You don't have to have the same values as people who get married, or people who don't get married, or whatever.
It may shock you to know that until relatively recently a woman's value and standing in society was intrinsically tied to the marriage she was in. They were wards of their fathers and their only method of a semblance of independence would be to marry and form a new household. The ceremony attached to marriage thus recognised that she had been elevated from being a dependent of her father to an independent woman. This is recent. In the past 150.years recent. It still happens extensively in patrilineal cultures. It is embedded and as memetic a theme as the crazy old lady, the overbearing mother in law, the clumsy passion of youth, the neglected housewife - the blushing, beautiful bride. These themes are deeply embedded into our society.
Why does it matter so much. Because...it does? Seeking to understand people's individual motivations is pointless because unless you share their exact point of reference there is little chance of you fully empathising. However, there will be rituals that matter a huge amount to you, which make absolutely no sense to anyone else.
Finally All marriages end one way or another. There is no benchmark of a successful marriage or relationship. Humans are fallible and change.
Don't threaten me with a good time, baby