My pet theory on this is that it's because most vulcans are vegan or vegetarian, and many humans still eat meat and other animal products. The diet thing is confirmed canon, but I can confirm being able to smell... meat smell(?) on people who eat it.
The meat Federation citizens eat isn't really an animal product. In the Orville, it's actually made explicit that killing an animal for food is regarded as tantamount to murder in the Union.
The reality is it wouldn't matter if it's synthetically produced meat, it's still going to have the same proteins and chemicals as it would if it came from an animal, which is what people (myself included) can smell on people who have consumed them. Eating garlic makes you smell like garlic, eating dairy makes you smell like dairy, eating meat makes you smell like meat.
I think the implication that we're smelling the concept of sin is very funny though.
except we have vegan meats made from various vegetable proteins that are basically equivalent at this point, and they most certainly don't have the same proteins as meat.
been eating meat my whole life and vegan nuggets are impossible to tell apart, and vegan ground meat is sufficiently close that you wouldn't notice being served it in a sauce instead of real meat.
I think we're arguing two different points. Chicken nuggets taste like breading, not chicken. And you can throw anything in sauce or chili and it's going to taste like the sauce.
Saying "if you cover meat substitutes in curry sauce or dip them in ketchup you can't taste the difference" is not the same as "meat substitutes taste the same as meat."
Impossible Meat was pretty good until twenty minutes later when I discovered my rare blood disorder makes me deathly allergic to the fake heme they use to synthesize blood. Seemed dead on identical to a Whopper, even the second and third and forth time I tasted it (from all the barfing).
I've had maybe two fake beefs that tasted dead on since then, and a bunch of fake chicken. I think since we have come this far in making fake meat, it's conceivable that there's a future tech that can craft a meat that doesn't cause the negatives of meat consumption.
I think it's also safe to presume that in the ultra future tech advanced society of Star Trek, they can remove the bacteria that causes body odor in humans.
I'm throwing in with the person who said that it might be cultural. Like how some people hate when I sweat garlic. And maybe Vulcans were too polite to tell humans about the unpleasantness of our odor since they logically know they shouldn't comment on this aspect of culture.
And also they seem to really get off on feeling superior, so why tell humanity there's something unpleasant about them? Those barbaric humans. I bet it's their illogical obsession with emotion that makes them smell (since certain emotions do in fact cause hormonal changes that make smells). "It's a biological side effect of unchecked emotion."
Of course, if that's the case, I bet they can smell Pon Farr. And you are welcome if you haven't had that idea yet, fanfiction smut people. (This is a joke. Y'all are a million steps ahead of me. You can see in my comment history I only this past week realized how homoerotic Q's obsession with Jean Luc has been all these years.)
I think it's also safe to presume that in the ultra future tech advanced society of Star Trek, they can remove the bacteria that causes body odor in humans.
A lot of odor-causing bacteria are actually beneficial for us though. And what causes Vulcans to experience that "odor" might not be coming from bacteria to begin with.. for all we know it might be one of the thousand of compounds that leak into the air we exhale directly from our lungs.
Virtually every gas or volatile liquid is susceptible to cause odor. The only reason we interpret pure water as odorless/tasteless is because water is everywhere so our senses evolved in a way that it doesn't trigger a response. There are many other compounds we don't really perceive because we are used to them at the concentrations that exist in our breath.
If let's say an alien species is not used to having 78% Nitrogen in their atmosphere, and they happen to have receptors sensible enough, then being in a ship with breathable air similar to Earth might just make them puke in disgust after having a sniff of what we might consider "clean air".
I'd argue it'd make more sense for everyone to wear the equivalent of a high tech mask (supressants?) rather than having to re-engineer the biology of the species every time they encounter an alien that might have a different set of compounds they might find unpleasant.