Waaay back in the day, that was also true of D&D. Int affecting what spells you could know was mostly a thing invented for AD&D 1e, and continued to be used up through 4th.
But you know what older editions of D&D also had? 0 level people. They weren't adventurers. They were the normal everyday people who did the labor to keep civilization running.
It wasn't until 3rd edition gave us the crapsack of NPC classes that made you wonder why NPCs didn't just pick any other class to be in the world. I mean, can you imagine why anyone would choose to be an Aristocrat over a Bard?
Truth is, NPCs shouldn't have class levels unless they're exceptional, like that retired barbarian who is now king by his own hand.
The implied setting behind D&D has changed every time the rules did. Sure, in 3.pf
, everyone should probably be a spellcaster of some stripe, except, there aren't rules for being a commoner with cantrips unless you multiclass.
Also, stat blocks would be a nightmare to write out. Can you imagine it? This NPC is 10 levels of Expert, 1 level of Sorcerer because he doesn't have enough Charisma to cast anything more than cantrips, and because his day job is making wagon wheels, he's somehow power leveled to 11th level by flooding the market with wagon accessories.
Does that really seem like a compelling setting to you? Does this seem fun?