This thread makes me fully aware that I'm not culturally an American! In Europe there are a number of legal/ financial ways of affirming couple-ness without a wedding. It's quite normal to do that, and often people who are anti-establishment about weddings or financially struggling take that course for the whole of their lives. Sometimes couples take that route, have their children grow up, and then have a big "getting married" party in their fifties or sixties to celebrate their union.

For example in France their is a civil solidarity pact PACS which you can find described in Wiki and this is very popular. "The PACS was voted by the French Parliament in October 1999, largely to offer some legal status to same-sex couples. In 2012, 94% of PACS were nonetheless between opposite-sex couples.
From a legal standpoint, a PACS is a contract drawn up between the two individuals, which is stamped and registered by the clerk of the court. In some areas, couples signing a PACS have the option of undergoing a formal ceremony at the city hall identical to that of civil marriage. Since 2006, individuals who have registered a PACS are no longer considered single in terms of their marital status; their birth records will be amended to show their status as pacsé."

PACS requires birth certificates of the couple and their parents as documentation but the parents/ family are not necessarily implicated in the ceremony. I also know many older French couples who are have the civil status of a couple but who never married (not sure how they did this). Children from those couples can take either/ both of their natural parents surnames.

Also in Europe even traditional Asian families are looking for ways to avoid expensive weddings because setting up a home together is more of a priority.

Traditions, and family obligations, against a private/ legal change of civil status. From my European point of view, I respect the OP and others for examining all the commitment/ legal options.