Sorry, didn't realize things from less than 6 months ago no longer counted.
E: For your more pedantic needs: https://www.steamprices.com/us/bundle/3100/paradox-grand-strategy-collection
Price goes up when sale hits, in order to pretend to be a bigger sale than it is.
You claimed that Paradox had raised the prices of the games for those who use USD in the last few months, which your own link proves to be false.
As for six months ago, yeah, when the price goes up for literally an hour, I'd put that as a glitch, not some sort of evil plan to get more money out of people. As for the winter sale price jump, that's super misleading in the graph, because what they did was discount the game and soundtrack bundle to the same price as the game by itself, and in the graph that's shown as the price changing. That's not a change in catalog pricing though, that's just a higher priced item getting discounted more.
As for the Grand Strategy Bundle, Its one of those Steam bundles where there's a permanent 10% discount on buying all four games, and the price goes down if you already own some of the games in the bundle. However, because during a sale the bundle gets a deeper discount, the price tracking website uses the total cost of the games as the price. That's not Paradox changing the catalog price, that's the way Steam bundles work. Its a little misleading, but that's more on the price tracking website and the way steam Bundle works than Paradox changing the catalog prices of its games.