Olive oil may be more expensive in general now because of poor harvests but at the time local production had been good and there was no reason to raise the price. The rationale? I guess it was profit.
Ye,s but prices are not just local. In general these are world prices as it can easily be imported or exported. Even more so within the EU single market which IS your national market.
On top of that its entirely normal for the prices of products that can substitute for each other to move together. If one oil goes up in price so will all the others. This is market forces acting as expected.
Sadly enough, the prices have stayed the same, although the demand has very likely normalized, now that people can buy "again" sunflower and other vegetable oil.