I think the issue in Mexico boils down to taxes. I remember @cardzard and @ROXANNE getting harassed during the 2015 scubaboard trip for bringing a bunch of soap to give away to those of us who attended. The locals were concerned about someone bringing in a product and selling it, presumably avoiding taxes/duties. You can bring in 10 packs of smokes, but if you're bringing a lot more than that, they probably doubt you brought it for personal consumption.That a moot point. this is not a cigarette issue. its a contraban issue and most travelers have no clue what is and what is not contraban. Some countries carbonated drinks are not allowed.
I don't think there's anything inherently wrong with a country protecting its revenue streams like that. Too bad the rules aren't a little easier to decipher for travelers. I suspect that if you use a travel agent, they could help with understanding those rules.