Unless they have a clear opportunity to create discontent
To influence elections in another nation, which nation would you pick to influence? The nation with fingernail-biting winner-take-all elections? Or the nation where each and every voter gets what they picked?
No surprise that Russia and China have very few opportunities to influence the elections in Sweden, the Netherlands, or Spain. Every voter gets the representative they hand-picked; there are no losing voters. This means there is little chance for China or Russia to influence the balance of power.
In nations with Full Representation, there isn’t all that much that China and Russia can do to influence the outcomes. There isn’t all that much upheaval when the Green Party gets 10 percent of the votes instead of 11 percent. There aren’t any parties that ever get 50 percent of the votes, so there is never any nail biting for the voters involved, just for the political parties in Sweden, the Netherlands, and Spain.
Only when there are truly divisive political struggles in place, such as the battle for independence of Catalonia in Spain, only then do the Russians and Chinese appear interested in getting involved via misinformation and support for the side that can upset the apple cart.
Sweden received a little bit of interest from Russia, partly because it joined NATO (once Turkey agrees to that), and partly perhaps because various parties declare beforehand who they like to cooperate with after the elections (though they are not required to stay within these bounds).
Take the US, Canada, or the UK, with their sometimes neck-and-neck differences between win and lose, and China and Russia grab their chances to influence the outcomes. Winner-take-all are easiest to influence because a single voter can make a seat go in the other direction.
China and Russia would love to influence all nations in the world, but particularly the democracies that give all seats just to the winners (and give absolutely nothing to the voters that picked the other candidates), those nations are easiest to influence.