Uhm actually... ;)

Letting the Danes take over, the alternative being enslavement and serfdom, stopped the raids. Not like our southern cousins appreciated us or the norwegians coming to "do unto others", right?

On the other hand, the reason why England was ripe for the taking is rather pertinent: weak central power with no real military of its own, dependent on locals in any given area mobilising their own militia under their local lords instead.

Same with Ireland until the irish united under one king to drive the northmen off the island.

Whereas Byzantium, Sicily and the moors all had strong central governement with a well-organised professional military - and happily traded with and even employed lochlannach.

(Sorry, lost the point somewhere.)