So ... the PCs
are special?!
It's the same with the Warrior class. There's no sensible reason anyone would be a Warrior instead of a Fighter, given that there are no actual prereqs listed.
This isn't real life, though, this is D&D. If your players have choices in their classes, the NPCs do too. Even if level 1 is set somehow by their background, they can always multiclass - especially if they're human. If you're a farmer or Janitor, you're a better farmer or janitor if you're using the mechanics of the Expert class. Or, heck, Rogue!
And I'd argue a city guard is a
better city guard if they're a Fighter instead of a Warrior. Advancing as a Warrior is senseless.
1e's 0-level makes better sense, if you need to stat out commoners at all - if you haven't adventured and haven't gained any XP from looting dungeons and killing kobolds, you don't have a level.
-O