It is market segmentation.
Airlines want to have larger profit as possible.
Old economic model tell you that there is an optimal spot between demand and prices (with higher prices you may get less passengers, but the passengers you have pay more, so possibly you gain more).
But since many years (initially on car rentals, then hotels), with more data, companies have found methods to "segment" the clients. So you may try to offer more expensive tickets to people who will pay for it (country, language, currency, and first number of a credit card are common methods, but now with web tracking us, there are more methods). If they offer cheap prices to the most rich nation, they get less profits. But with higher prices, you may increase the income, but you will have empty seats, so you offer them on other markets (which should not effect prices on the main market).
Note: market segmentation is also a reason of business ticket prices (also on economic class: more flexibility, more price, but you are in a business travel). This is also the reason why you may find flight with stop-over more cheap (e.g. A to C via B, but just A to C or also B to C are more expensive): some people can afford to pay, but you can fill the airplanes without need to reduce prices for the first group.
Note: For flights (and car rental and hotels) this is the norm, and nobody complain. Amazon 15-20 years ago tried a similar method for book, but it had to suspend itquickly: people were not "ready" for such segmentation.