There is no biological reason because weddings are a social construct we made up in the first place. Not every human society even has weddings/marriage as a concept. It’s just purely societal conditioning that teaches little girls that marriage and having kids is the only future they can expect. I was never interested in marriage as a young child (duh), but my mother always talked as if that future was inevitable for me. It’s hard not to think about something everyone treats like fate.