Why is it 'Next of Kin' instead of just 'Kin'? [closed]

From Merriam-Webster's definition of next of kin (emphasis mine):

: one or more persons in the nearest degree of relationship to another person

Taking that meaning and inserting omitted words (in the particular context of a death), it can be paraphrased as follows:

• Next ^{[in line of inheritance and responsibility]} of ^{[the remaining]} kin.

It's not talking about all of the person's family and relations (which would simply be kin), but only those who are the closest to the deceased. Legally, it would only be those who have some kind of responsibility or duty to take care of with respect to the person.

For instance, a spouse, sibling, parent, or child would likely be included in the next of kin. A cousin, especially one who had not spoken to the person in many years, likely would not be.