Maybe pre-nup has a different meaning where you live. I'm in the US, and here a pre-nup is an agreement that defines custom rules for a marriage and divorce that are override, add to, and/or clarify the rules of the default marital contract. So, not everyone has one.
Wikipedia defines it well:
> Couples enter into a written prenuptial agreement to supersede many of the default marital laws that would otherwise apply in the event of divorce, such as the laws that govern the division of property, retirement benefits, savings, and the right to seek alimony (spousal support) with agreed-upon terms that provide certainty and clarify their marital rights.
Wikipedia defines it well:
> Couples enter into a written prenuptial agreement to supersede many of the default marital laws that would otherwise apply in the event of divorce, such as the laws that govern the division of property, retirement benefits, savings, and the right to seek alimony (spousal support) with agreed-upon terms that provide certainty and clarify their marital rights.
https://en.m.wikipedia.org/wiki/Prenuptial_agreement