You're working off the assumption, the opinion, that Wizards will make a point of avoiding complete character race builds whenever it's possible for them to turn that race into a variant of something already available. When that's not been their design philosophy for the overwhelming majority of new character races in 5E. When there are commercial reasons for them to do complete character race builds, as with the leonin.
The only thing Wizards has indicated will be changing is that future character race options won't have default ASIs. So until Wizards starts actually releasing products that studiously avoid full builds in favor of variant after variant... you'll forgive me if I'm going to expect them to follow previous patterns.
(There's also one more reason they would continue to do complete races or subraces: to continue the PHB+1 approach for Adventurers League. Telling you "this new race is kind of like kobolds, but change this" is useless if you can't also reference that other sourcebook. In fact, this may be another reason the leonin wasn't a tabaxi variant.)
The PHB + 1 Angle is one that I hadn't considered, and that actually makes a lot of sense to me as a potential reason.
Because while you keep saying that there design philosophy has been to make new races whenever possible, it really hasn't been. Pretty much every time they reference elves, dwarves, goblins, and orcs in a new setting, they wither reprint them or at most they give a variant.
And I think it is fair to look at the books like this as well.
PHB ->
Dragonborn, Dwarf, Elf, Gnome, Half-Elf, Halfling, half-Orc, Human, Tielfing
Elemental Evil ->
Goliath, Genasi, Aarcrockra
Volos -> Goliath (reprint),
Aasimar, Bugbear, Firbolg, Goblin, Hobgoblin, Kenku, Kobold, Lizardfolk, Orc, Tabaxi, Triton, Yuan-Ti
Ravnica -> Human (PHB), Elf (PHB), Goblin (Reprint),
Centaur, Loxodon, Minotaur, Simic, Veldalken.
Eberron -> Dragonborn (PHB), Dwarves (PHB), Elves (PHB/Sidebar variant), Gnomes (PHB), Goblin (Reprint), Bugbear (Reprint), Hobgoblin (Reprint), Half-Elf (PHB), Hafling (PHB), Human (PHB), Half-Orc (PHB), Orc (Reprint), Tieflings (PHB)
Changeling, Kalashtar, Shifters, Warforged
Theros -> Human (PHB), Centaur (Reprint), Minotaur (Reprint), Triton (Reprint),
Leonin, Satyr
So, I think your hypothesis about the PHB + 1 is dead on. If you are in the PHB, you don't get a new write up usually. IF you were in Volos or Ravnica, you get a reprint. And then if you look back, they rarely repeat concepts after that. There is very little overlap in concept with any of these.
Which gets to my second point, and the one that is more a prediction and gut than anything I can back up with evidence. And that is, we've got them all. See, it is really easy to look at the PHB, see Volo's and go "aha, they will create more races, they did it here! And they did it in Eberron!"But the problem is, now that they have those races, they don't need to recreate them. I mean, if you wanted to make the Magic the Gathering Setting of Mirrodin, which is covered in constructs, do you make new races? Or do you adapt the Anvilwrought background, Warforged, and Reborn mechanics instead?
I find it very telling that in Theros they made the Anvilwrought a background choice, instead of a race. They could have made space for a new race there, but they went a different route. And I think going forward, since we have already covered so many different options, they are not going to be making as many new races.
Default ASIs only give you an "obvious decision" for the ASI for your character race. That's all. Not everyone is thinking about their race-class combo, or specific builds, or the like, when they make a character. Sometimes they pick their race, and then their class, and then their background, with only brief consideration, if any. They might choose their class because it's the archetype (elf wizard), they might choose it as an anti-archetype (elf melee fighter), or they might choose something because they just think it's neat (elf warlock). And quick builds are useful to folks like that, because they can just say, "I go with the default", and get to gaming. While that may not be the way you or others design characters, it works perfectly fine for some players.
Dude, I get that. What you aren't hearing is that if you say "I want to go with the default elf" then you still have to pick a class. You say Elf Wizard is the Archetype, but Elf Ranger is an archetype to. So is Elf Arcane Trickster. Elf Monk.
You have declared that Elf Wizard is the archetype, but nothing actually backs that up. That is what Faolyn was trying to get across to you, the guy who wants to play the "archetypical elf" but doesn't want to think about their ability score placement still has to think about their ability score placement.
Do you play a High Elf for +1 Int? Does that mean you play a Wizard or an Artificer?
Do you play a Wood Elf for +1 Wis? Does that mean you play a Ranger or a Monk?
Do you play Eladrin for +1 Cha? Does that mean you play a Warlock or a Bard or a Sorcerer?
Do you play a Sea Elf or a Shadar-Kai for +1 Con? Does that mean you want to play a ranged character, a rogue or something else?
It is actually almost hilarious to use elves for this example, because the only score you can't increase via elf is Strength.
And sure, maybe you pick you class first. You want to play a fighter.
Do you want to be melee or ranged?
Ranged fighters can be archetypical for elves, halflings, goblins, kobolds, bugbears, tabaxi, human, half-elf, changeling, warforged, air genasi, satyrs
Melee fighters can be archetypical for Orcs, half-orc, human, dragonborn, minotaur, goliath, firbolg, warforged, half-elf, changeling, earth genasi, leonin,
I'm not trying to say you are wrong that some people don't care and just pick things, but you are also trying to sell that they don't care and pick things, while simultaneously finding it too much work to just pick ASIs, because they want to play for or against type without having to choose. And I think it is fair to question that assertion when you remember that the ASIs alone have overlap with multiple classes.