IMHO, I think "Why not Dex?" goes back to the four iconic classes sort of occupying four figurative corners, where wizards (or magic-users) and fighters were diametrically opposed, as were clerics and rogues. So, fighters typically had high Str and low Int, wizards had low Str and high Int, rogues had high Dex and low Wis, and clerics had high Wis and low Dex.
I can't say I've seen any designer put in print that this was the way it was set up, but it always seemed that way to me.
"Why not Int?" really is about "Why Wis and Cha?"; the answer to the latter should be obvious, but there's also no particular class need for a cleric to be able to buff Int.
--Axe