Week Twenty Five: Why is there an alphabetical order?
Monday, August 19, 2013 at 9:03AM in Week 25 
But why? WHY?!
I honestly still don't know. And without the project I might never again have thought to find out.
Alphabetic order as an ordering device has been already used in the 1st millennium BCE by Northwest Semitic scribes using the Abjad system.[1] The first effective use of alphabetical order as a catalogizing device among scholars may have been in ancient Alexandria.[2] In the 1st century BC, Varro wrote some alphabetic lists of authors and titles.[3] In the 2nd century AD, Sextus Pompeius Festus wrote an encyclopedic work with entries in alphabetic order.[4] In the 3rd century, Harpocration wrote a Homeric lexicon alphabetized by all letters.[5] In the 10th century, the author of the Suda used alphabetic order with phonetic variations. In the 14th century, the author of the Fons memorabilium universi used a classification, but used alphabetical order within some of the books.[6]
In 1604 Robert Cawdrey had to explain in Table Alphabeticall, the first monolingual English dictionary, "Nowe if the word, which thou art desirous to finde, begin with (a) then looke in the beginning of this Table, but if with (v) looke towards the end."[7] Although as late as 1803 Samuel Taylor Coleridge condemned encyclopedias with "an arrangement determined by the accident of initial letters",[8] many lists are today based on this principle.
So I guess the answer is "We've just always done it this way for as long as anyone can remember." Groovy.
Make what you will of this. We're climbing back up the word count minimum ladder: 200 words, Sunday, that's my fun day.