Comment by RussianCow

While I agree with the overall sentiment here, it's worth noting that businesses use contracts because trust between two parties can never be assumed—both businesses are purely acting in their own self-interest. On the other hand, with marriage, it's generally (hopefully) safe to assume that both parties trust each other fully before entering into the agreement. Whether and how that plays out in practice is another story, but IME, very few people enter into marriage prepared for the case in which it ends. This is why prenuptial agreements can sometimes be a touchy subject, since it breaks that assumption of complete trust.