Pokémon Movepool Oddities & Explanations

[CPU]

You would think that's it, but, by generation:
Charmander, Charmeleon, Charizard, Blastoise. Why do any of the Chars get it, and why Charmander but not Squirtle if we had to pick a pre-evo?
Typhlosion(and H), Feraligatr. Because screw Meganium, amirite?
Sceptile, Combusken, Blaziken, Swampert. Fighting-type justifies Combusken but no other pre-evos, sure. But Swampert breaks the trend of only bipeds getting the move, and seems...less suited than most of the other options(this is pure vibes). Sceptile is at least the first grass-type starter to get it.
Monferno, Infernape. Again, fighting makes sense. Why is Empoleon the first water-type to miss the move?
Pignite, Emboar. Again, fighting.
Chesnaught, Delphox. Psychic and fighting, fine. But the dark-type projectile-focused ninja doesn't get it?
Decidueye H(not A), Incineroar. Basically a fire/fighting, fine. Though again, both of the other starters are more focused on ranged attacks with mental powers than he is, which is odd.
Rillaboom, Cinderace. ???
And no starters in SV get it, which makes the first time the fully-evolved fire type cannot learn the move.

Like I said, I think there are various explanations for what does and doesn't get the move, I just don't think any of those explanations are consistent with each other.

Charmander and Charmeleon learning the move is new to Gen 9; a quick comparison of the move's distribution from Gen 8 to 9 shows some slightly increased availability (in addition to the littler Chars, both Gravelers and Elekid get the move for the first time in Gen 9, for example).

I think there's definitely some intention for the move to be a Ki blast; having hands (or at least arm-adjacent appendages that one can bring together) is nearly a prerequisite, though one that some Fighting types skirt around (the Swords of Justice and Falinks).

The distribution requirements, inconsistently applied though they may be, seem to me to be:

1. Hands/Arms to, well, focus the blast
2. Being fully evolved to have the mental fortitude to fire a Ki bomb
3. Being Fighting type (or Fighting-adjacent, which is my logic for Graveler/Elekid, among others) may let a Pokémon bypass the first two requirements (being a Legendary/Mythical might help too)

I don't see a Pokémon being focused around ranged/projectile attacks impacting what learns it except in some rare cases (Clawitzer, maybe Yveltal?). Addressing some of the starter anomalies you brought up:

• Swampert is capable of attacking bipedally, at least, and it learns Hammer Arm by level (I actually associate this move with Swampert for whatever reason).
• Not exactly sure why Empoleon doesn't get it; I guess GF decided its claws on its flippers weren't handsy enough.
• Greninja not learning Focus Blast does seem weird at first glance, but as a ninja it's more suited to covert attacks, not a big flashy energy shot. Its Dark type may also provide a reason why it doesn't get the move; perhaps it's not "pure of heart" enough (other Dark Pokémon can learn the move, though [again, Yveltal], so this is a flimsy conjecture).
• Immediate counterpoint: Dark-type Incineroar. But, as you mentioned, it's a Fighting type in spirit, and as it's based on a wrestling heel, it could also just be "playing the villain."
• I would assume that A-Decidueye, Inteleon, and Meowscarada don't get Focus Blast for the same logic that Greninja doesn't: they're designed around sneaky, out-of-sight attacks, despite having hands. Hard to say if H-Decidueye gets it because it's a more aggressive attacker or because it's a Fighting type.
• I have no idea on Quaquaval. Maybe it's too caught up in dancing to be able to charge a Ki blast

Just gonna close this out with my personal weirdest pick for what learns Focus Blast: