I know what it is from anime and media, but why's consummation a thing? like what does sex have to do with marriage at all?
[I'm genuine in my confusion. the questions aren't rhetorical.]
it is a historic cultural thing. historically from decades to centuries ago, marriage is not about love but of necessity, reproduction, having heirs and/or helpers to take care of you once your health fails in old age.
This is common across plenty of Europea and Asian cultures. Hence the stuff about virginity, purity, motherhood, or marriage consummation across cultures and centuries that do not even share languages.
Thankfulky outdated customs don't apply as heavily, so love matters a lot more, so close relationships and sex happens before marriage usually. NONE OF THAT ARRANGED MARRIAGE BS. shame 14 yr olds are still married off in arranged marriages in some backwater places...