Depends on the resource and some places on the globe are better for growing things than others. Cocoa and vanilla are notoriously hard to transplant and only do well in certain areas while tea and coffee can be grown just about anywhere in their climate zone though they might not taste as good as other areas. Some areas are better at producing horses while others better at producing sheep and high quality wool. Think of the tiles those resources appear on as the best spots in the world to produce that resource.
Yes, it depends on the resource. But, as well as some resources need a particular climate/soil, others can spread anywhere in temperate climates, like corn, wheat, horses, cows chickens and pigs. Additionnally, one can spread out its regional resource into a worldwide commerce by massively transforming the land, example : palm oil. I know plantations, especially the way they look, already kind of represent that, not to mention their gold output, but it could be more vast and ambitious than simply that.
"Normal" farms are already supposed to cultivate "something", because well, without resource you can't make farms, but it would be nice to specialize any farm, with various bonuses. You need gold ? Plant corn. You need more food ? Plant wheat. You are surrounded by marshes ? Plant rice ! Of course you should have access to them, and be able to grow them, but you may have need an alliance with another civ in order to trade this kind of things.
It's not true that you can mass product a resource only in its native environment. As to quality, it's not always, if not never, true either. As to reputation, I recognize this is the hardest thing to change about a resource. And that would be the strongest argument in order to not been able to duplicate resources, "we both have wine but yours is Champagne, I want it". But the reputation of corn or wheat ?