Potatoes were first cultivated probably in Peru (in very small mountainside fields), but the varieties normally made into french fries would find the climate and open terrain more suitable in parts of Argentina and Chile. Also, large-scale french fry manufacturing plants (like we have here in eastern WA) are very expensive.
I’m sure the local McDonalds there could purchase some potatoes locally, some hand-operated french fryer cutters and proceed to make up fresh daily batches.
Heck, they could probably hire a Mexican to come in every morning and slice them up for cheap!