Encyclopedias haven’t always been alphabetical. The structure of a medieval encyclopedia was hierarchical, reflecting a divinely ordered universe. Begin with God, then human beings, animals, and on to inanimate things. The change to alphabetical order, Judith Flanders argues, marks a change in worldview. From A Place for Everything: The Curious History of Alphabetical Order (New York: Basic Books, 2020):
Just as the spread of alphabetically organized dictionaries and indexes had indicated a shift from seeing words purely as meaning to seeing them as a series of letters, so too the arrival of alphabetically ordered encyclopedias indicated a shift from seeing the world as a hierarchical, ordered place, explicable and comprehensible if only a person knew enough, to seeing it as a random series of events and people and places.As Flanders also points out, Wikipedia is an encyclopedia that makes the principle of alphabetical order moot.
Also from this book
On “the preeminence of ABC” : Meaningful letters : Pen and paper and