You can just decide potatoes developed there naturally.
Hard disagree with this. Potatoes as an energy rich, nutrient rich, non-perishable, ultra-fertile super-power crop are simply not fucking "natural."
Why this mindset is inherently racist, a history lesson:
In the North Americas, nomadic tribes tended to "natural" gardens that they harvested all year round. They moved from garden to garden for each harvesting season. They did intensive cultivation of the landscape but it involved things like cutting away dead branches and not ripping up an entire plot of land to destroy the whole soil layer. Human intervention actually prevented further soil erosion and helped create a (superficially) undisturbed looking biotope, that actually thrived under human domestication.
(This is for any clowns who keep saying "We are the virus - nature is healing": This ecofascism ignores how native and harmonic farmers can instead enrich the biosphere instead of exploiting it. American soil also does not support European-style agriculture, that's how you get the fucking Dust Bowl and why USAmerican farmers are now trying to adapt Native American techniques to combat the natural disaster their colonist ancestors created in the first place.)
Then the Europeans came, gazed upon these beautifully cultivated gardens, where you could walk from one fruit-ladden branch to the next and called it: Paradise. They did not see the careful human hand that had created it, for it was from a culture invisible to them. God's creation erased humanity's creation, their agricultural expertise.
The lazy savages were so lucky that they lived in the literal Garden Eden, where they didn't have to toil like proper Christian farmers. How fucking lucky and undeserved of them! Surely us civilized, hardworking farmers deserve this natural, untouched land more than them! Initiating Genocide.exe...
Why the potato exists in the first fucking place:
The Incas lived in a horribly mountaneous region with fuck all to eat. European-style Agriculture is horribly impossible to achieve because the soil dries out easily in the mountains and gets flown away. There's a reason why the Inca developed these amazing watering systems and stair gardens and it's not because they fucking looked pretty! But because they were necessary.
The potato was specifically cultivated to grow in all kinds of soil because fuck all else grew there. You know how in Andy Weir's The Martian, the protagonist literally just survives off of growing potatoes and tomatoes (and later only potatoes) in Martian soil? That's not going to happen with any two random European crops. Probably not even ten or twenty of them, because they take too long to grow or won't grow in the first place. Or he just doesn't know how to grow them. With potatoes, you plop them in the Earth/ Mars and you're done. Strand him on Mars with lettuce and carrots and he fucking dies of starvation. End.
The Inca were simply playing agriculture on hardmode compared to Europe. Literally just compare the list of domesticatable animals: Cows, pigs, sheep, goat, horses, donkeys, as well as dogs and cats (probably more I'm forgetting).
What do the Inca have? The fucking Llama. Which is why the Llama is similarly utility-stacked compared to the potato: It gives wool like a sheep, milk and meat like a cow, can be ridden like a horse, carry goods like a donkey, traverse mountains like a goat and guard like a dog. Give it a couple hundred thousand years and a bored homo sapien and it's going to catch mice like a cat too.
The biodiversity of domesticatable fauna and flora pre-human cultivation is simply higher in Europe. There's literally no need for some ancient farmers to perfect one single crop, when there's so fucking many to choose from. It makes zero evolutionary sense. We've had starvation events in Europe but we've also had the potato blight, which is going to happen if you do mono-cultures and invest in only one crop. Trust me, if the Inca could have lived in an area that supported our bio-diversity, the potato would simply not exist.
It's basically the same reason why in Alien, Xenomorphs can't be naturally evolved because they're beyond apex predators - SSS tier. Mother Nature doesn't care about perfection. It sees "Good enough" and lets you pass with a C- at best. Potatoes are the crop version of xenomorphs.
If I see potatoes in your fantasy story, there better be some fucking apocalyptic extinction event or radical biotope transformation pre-whatever medieval timeline you're writing or you just don't understand anything from evolution, cultivation to colonialism and I will be saying so.
Like, write the fucking fantasy potatoes, you fucking assholes. But write them well. Understand and research evolutionary forces and be creative.
Lazy worldbuilding is not only lazy worldbuilding - it can also be racist. I don't know why I have to keep telling people to stop being either and then I'm the one getting clowned on for it.