Understanding Engaged

I dont undestand being engaged. I understand I love you. I understand I want to spend the rest of my life with you. I don't understand why we ask a person to spend the rest of our lives with us and then make them wait a year to do it. If we aren't ready to get married why do we ask?
I don't do well in gray areas and engagement just feels like a big holding pattern. I'm feel like I'm sitting in a plane out on the tarmac.

I also don't understand a wedding. I understand a marriage, but I don't understand spending a year of my life focused on one day. I don't understand spending thousands of dollars on something that will virtually be over in the blink of an eye (after you wait the year to actually blink your eye).

I don't understand how something that is truly only about two people becomes about everybody else.