That could be because the rules for HD are either in the Player's Handbook for PCs or in the Monster Manual for NPCs and Monsters. Why would it be in the DMG?
I don't know, why would it?
I listed these same stats in an earlier post, got them from 5e tools, but compared them directly to the numbers provided by DnDBeyond, which I checked for context.
I don't have a D&D Beyond subscription, but I am capable of searching the monster list. The only official, non-homebrew commoners I can find are the generic commoner, the lizardfolk commoner (which has issues, as both
@Faolyn and I noted), and two others: a goblin commoner and a kobold commoner, both from Tales from the Yawning Portal. Since I have no subscription, I can't determine whether they conform to the DMG guidelines, or Volo's guidelines, or if they're just using the default commoner stat block.
That said, if they do use the generic commoner stat block, that simply means racial traits weren't applied. Also, D&D Beyond isn't infallible, either (though I would agree it's more reliable than 5etools) and has had unofficial stuff under its aegis (such as that racial feat supplement they released on DMs Guild years ago).
The Lizardfolk in the DMG get +2 str, -2 int, in Volos they get +2 Con, +1 Wis
The Kenku in the DMG get +2 Dex, in Volo's they get +2 Dex, +1 Wis
The hobgoblin in the DMG gets nothing, no score increases, in Volos they get +2 Con, +1 Int
The Deep Gnome in the DMG gets +1 Str, +2 Con, in Mordenkainen's they get +2 Int, +1 Dex
So, we are up to at least seven "monstrous player races" that are innacurate between the DMG and their published versions. That is approaching 25% of all races.
And as I pointed out, that may indeed suggest that "PCs are special" had begun to emerge as an idea sooner than 2020. Or it may just indicate that they had a rethink on their baseline ASIs. Either way, it doesn't have any bearing on how they treated ASIs in the core rules - as a trait that was part of the race's makeup.
If using it straight from the book is the "non-custom option" then how is that expecting you to customize it? There is no where where it says you are expected to customize the statblock with ASIs and traits. It says you can.
Choosing to customize =/= the default.
Then I reiterate the question I asked
@Faolyn - if you assume that a generic commoner is meant to represent a member of a nonhuman race as is, does that mean elf NPCs don't have darkvision? That dragonborn NPCs don't have breath weapons?
The only interpretation that makes sense here is that you can use the NPC statblocks as is if you don't want racial traits factored in, or you can reflect their race by applying the racial traits from the PHB or DMG.
And for the halfling he has, and will always have, the 5e PHB to tell him what defaults to use.
And for the Goliath he has and will always have, the 5e Volo's guide to tell him what defaults to use.
And for the Changeling he has and will always have, the 5e Eberron guide to tell him... that they get a +2 Cha and that the other stats are floating.
And for the Human he has, and will always have, the 5e PHB to tell him that it is always floating and there are no defaults.
So, if changelings and humans aren't bad, why is the Lineage #6, the future product he wants to play, bad? It won't have a default? False. It will have the same default every race with floating scores has, that is that the scores are floating. That is their default.
First of all, when did I say floating ASIs were "bad"? I already said I don't really have a position on fixed vs. floating. I just want continued support for fixed ASIs as well, so folks who liked having defaults for character races can still get them.
Second, humans don't count for this discussion, because only the variant human has floating ASI in the core rules. The default human gets +1 to all six stats. If you pick variant human, you're already not a casual player, you're looking to customize.
Third, it is true that two existing races have partial floating ASI - the changeling and the half-elf. However, those both still provide some partial guidance for folks who want it, which is better than zero guidance. (Also, now I wonder how popular the changeling and half-elf are with casual players.)
Fourth, sure, Wizards is perfectly capable of establishing a character race so adaptable and formless that it wouldn't have any typical ASIs. But so what? You're still making things more complicated for folks who liked having suggestions. (In fact, similar to changelings and half-elves, I wonder how popular such a character race would have been with casual players.) I don't see the harm in throwing some recommendations in with them.