Answer. Fuck, whatever.

The math part has an easy question.

These are excellent questions, and one should take them on vigorously outside the shower. And consider related questions, like: Why did most Westen Hemisphere cultures (all, afaik) had NO alphabet. Some had counting symbology. and some rudimentary quasi-standard pictograms, but no real alphbet. Or why did the Romans use the complicated system of Roman numerals? And were the picto-glyphic wrtten languages of Ancient Eygpt and also that of China preceded by a phoentic alphabet, and if so why was it replaced?

Then there are meta-questions: can these questions be answered, and to what degree of accuracy? The past is always befogged! Some think they discover some stones, or ancient papyrii and solve it. Take a paltry amount of artifacts, and queasy bits of "dating" technology and combine arrogance and we'll have many false certainties paraded as utter holy truths.

But why did they put the alphabet in alphabetical order?

Sorting libraries is all I can think of.

Answers:
Alphabet -> The Phoenicians
Numbers -> The Arabs & Persians
Math -> The Arabs & Enlightenment Era Northern Europeans