Just a random thought that popped into my head.
The original order of the six ability scores:
Has S/I/W first because those were the prime requisites classes presented in OD&D, Fighter/Magic-User/Cleric. Gygax also used the Thief, which is why Dex comes 4th.
Was it assumed that classes with a higher prime requisite in the order would be more common? Seems obvious that Fighters should abound. Were Magic-Users assumed to be the second most common class, then Clerics, and Thieves being a bit rarer?
Thieves, rogues, and scoundrel types are more common in the source literature than Clerics, but then Clerics made it into the original rules set, while Thieves only made the first supplement.