I know that they aim for good and easy loot, it's just that in other games I need to push them back at least once in a while.
I suspect the fact that the norse are mostly united in three realms (Svipjod, Sjaelland and Ostlandet) makes them more focus on infighting or warring against Karlings.
Here's the map :
Talking of Karling, Karloman survived to 65 though seven months before Charles. The latter only conquered Saxony during his life. After the death of Charles the realm split in three (Saxony, West and Middle Francia). Bad thing then happened to West Francia. Frisia revolted, Lombardy used the occasion to spread over the Alps and I waged a small war for a county (The Duke of Anjou is from my dynasty and I made a small mistake with succession law.) Then the West Francia king died and the kingdom splitted one more time to create Aquitaine.
So for now western Europe is split between 4 Karling kingdoms, a united Frisia, an expanding Lombardy and Bavaria.
Central europe has some kingdoms formed but the more interesting are Poland and Croatia. The first is entirely Slavic except the capital, which is now catholic because the King of Poland converted, the second is ruled by a slavic king, but outside his demesne the country is a mix of Catholics, Orthodoxs and Tengris.
Edit : Forgot to mention my surprise to see Northeast Finland under Estonian control. Poor Estonia really wants to be a nordic country...