In most places in the world, being married often comes with a variety of legal protections and benefits that aren't all as easily granted to other classes of persons, such as:
Improved tax brackets
Inheritance and custody rights
Financial and attorney powers
Visitation and healthcare rights
Visas and paths to citizenship
Some places also have the concept of a "domestic partnership" which has a subset of these privileges, but cannot be granted all of them. Likewise, various family members usually have limited access to some of these. However, no type of relationship gives the same potential as marriage, as far as I know.
Resolves YES if, after the creation of this question, any country removes all distinctions and protections for married persons from law, makes marriage illegal, voids all marriages in the country, or creates paths for all such benefits to be equally accessible to some other form of interpersonal relationship(s) (family, friends, domestic partnerships, etc.). A country that formalizes any such changes for a future date, even if that date is after 2029, does count so long as the decision was locked in before 2030.
May resolve to high PROB if rights (and paths to granting rights) are significantly equalized, or other YES criteria are largely but incompletely fulfilled. This would likely happen after close, so that opportunities for a full YES remain.
Otherwise resolves NO after close.
Non-human legal persons don't count for the purposes of this question.