Merriam-Webster, copied in for reference.
adjective
Of or relating to health or the protection of health.
Free from elements, such as filth or pathogens, that endanger health; hygienic.
"sanitary conditions for the preparation of food."
Of or pertaining to health; designed to secure or preserve health; relating to the preservation or restoration of health; hygienic. See the Note under sanatory.
"sanitary regulations"
See under Commission.
Of, or relating to health.
Clean and free from pathogens; hygienic.
Free from filth and pathogens.
"a sanitary washroom"
You're right, there is a usage of it to mean "healthy" in general, my bad.
However, I hope you can understand that it isn't the most common usage, and that the bulk of the definitions and usages are pathogen related. Hence me either forgetting or not having run across its more broad usage.
I'd still use a different word, but I definitely agree with your point under that usage :)
That being said, sometimes something that's not sanitary (using the general definition now) may still be the better option than something that's worse.
Which is the case here, imo.
When you're dealing with something like a soda/cola, you're very often dealing with a slightly corrosive liquid. When that's the case, you're limited in what you can use to ship and store it in. Glass, obviously, is the superior choice in terms of maximum safety for chemical exposure. It is also much more expensive to ship, and has more bulk for storage. It also has a different kind of safety issue; the extra weight and the risk of damage leading to injury rather than just a mess.
The problem is the lack of choice for patrons. We can't say "give me a glass bottle instead" and get one. It's out of the bag-in-a-box or nothing these days.
As far as comparisons to other potential chemical exposures, the ones you listed in specific are a personal choice to take in at all. Whereas sodas, people might not be aware of the fact that they're served from plastics. That doesn't negate your point, it's just an interesting distinction. The plastics in food storage is more like second hand smoke than smoking because it isn't something you can explicitly choose to engage in, and opting out is problematic.
Mind you, I'm not certain that the plastics leeched into a soda are at a high enough level to be worse than the soda itself. They're distinctly not sanitary, no matter what they're stored in. Too much sugar, too much acidity, too many colorants and flavorants that are either neutral, or haven't been excluded completely as possibly unhealthy. Just the caffeine levels in them are problematic, and the problems from the sugar levels will show up in your body years ahead of the plastics. But, again, you're choosing to drink them, but may not be aware of the plastics to opt out.
Fwiw, my household has phased out plastics entirely for anything that gets heated, and for long term storage. We just don't buy new containers as they reach end of life, and any food that comes in plastics gets moved to one of our glass or metal containers if the product is going to be sitting around for more than a week or so. Longer if it's a dried product, since leeching rates for those approaches zero in anything under years. Which is only relevant so you understand that I agree with you that there's no such thing as a totally food safe plastic.