Zoro and Sanji were doing fuck all in the east blue before they met Luffy, with dreams that don't really involve conquering any countries or even challenging the government/Yonko even. There's no real reason for them to have it other then the fact that they have to become top tiers in their early 20s while you have guys training for decades.
??
Zoro was pursing WSS, already had made a name for himself on his own and had more infamy than Luffy in EB, had some dudes following him, and killed Mr 6 (IIRC). By the time he joined up with Luffy.
And said to Luffy to his face that he would kill him if he stood in the way of his goals.
The reason for admirals and sanji not getting is not based on story or being mad oda for being at "rules of coc" for the 99% but on agenda
if you made 1 million post on them not getting coc and wrote haki desertation you obviosuly gonna get clowned on
This is also one of the rare agenda brainrot things that goes beyond this forum this is a point where probally most of the powerscaling fandom would take their biggest L
Remeber couple years ago people were saying YC 1 = admiral and Ling = Eos sanji

People memory holed that shit because how stupid that is
Nah it isn't. If you think it's 99% agenda driven, it's probably based because you've been playing in the agenda mud for too long lol.
I don't think it's agenda driven, but factual, to argue that Oda himself has played into the persona and ambitions of conquerors several times in the series. But he also isn't playing into this line of thinking a 100%, Koby is a great example here.
This was my take on the topic in the spoiler discussions.
At this point, yeah it's arguable that a strict pattern is no longer a thing.
But let's be honest, Oda did really play into the "kingly qualities" thing multiple times. Played into "personalities" of conquerors etc.
There are many cases where this was blanantly stated in manga. Stuff like those guys aren't the type to work under others, would tend to squabble if put together, unreasonably stubborn, indominable spirits, etc.
Whitebeard used this line of thinking to even deny crew membership to Oden.
It didn't help that the poster boys of conquerors - Roger, the OG Yonkos and the 4 new gen conquerors (Luffy/Ace/Zoro/Kid) perfectly fit the description as well. Unreasonably stubborn and prideful knuckleheads.
One can't fault readers who chose this interpretation really.
I think it's a mix of both. Oda wants to have his cake and eat it too (unsure if this is the correct analogy lol).
Oda wants to use the persona argument when he wants to (especially when he wants to do something like highlight the persona), but sometimes he just hands it out to whoever just cause he wants to (like Koby)
It's the persona and ambitions narrative that was used by those who pushed Zoro to have conqueror's haki, not parallels or anything; this was before there was even any direct powerscaling implication here (for a decade+ conqueror's haki was simply fodder control and just indicated potential).
Just to address the OP meanwhile, Jinbe and definitely Ussop of course shouldn't have conqueror's haki. Jinbe is a 46 years old veteran, too late for that. Ussop especially having it would be dogshit writing and kill the entire thing, might be a drop worthy event even.
Coming to admirals.
It's a case by case basis with admirals. I'd say Akainu, Aokiji and Fujitora would be in sync with the "persona" narraive as well. While Kizaru is a mixed bag (leaning towards no for me), and Greenbull is heavily leaning no.
Issue is that there is no indication that any admirals have it, so far. That should however not be used as a confirmation that admirals won't or can't have it obviously, esp the 3 I mentioned above.
And there is a powerscaling argument also here, in that admirals have such insanely powerful DFs that they don't
need advanced conqueror's haki to reach top tier as well, but that has zero relation to the persona arguments of course.
I'm not a fan of Sanji having conqueror's haki either, due to the persona narrative. Nothing to do with powerscaling, Oda can always upgrade his fire powers and exoskeletons as needed to made Sanji close to Zoro in power.
However, if Koby can have conqueror's haki (it isn't 100% confirmed yet but honesty impact might have been advanced conqueror's), I see no reason Sanji can't.