Right? The engagement is more important, it's what matters more for the couple and the marriage is what matters more for everyone else, friends, family and the law.

For example, in terms of commitment, not much changes for a couple after they're married. They were 100% committed to each other at the time they agreed to get engaged. What changes after a marriage is more how other people see their relationship and it matters quite a lot in terms of their legal status as a couple.

If you've agreed but are on the fence leading up to the wedding, the wedding isn't going to change your mind.

If there wasn't a legal requirement or a social incentive to have a ceremony, people would just get engaged and start referring to each other as their wife/husband.