In Normande they sound got franconized. Ditto in Sicily etc.
their culture was "lower" in terms of literature, art etc. compared to the Roman based cultures so they were easily absorbed. In England they influenced but even there were absorbed.
Yet the Geats and Swedes and Danes also included farmers who stayed behind -- the more intrepid migrated while the ones left were not quite so brave.
However all of that is irrelevant to why modern day Swedes are the way they are -- after all all barbarians get civilized and "weak" -- look at the Stoic Romans who became the sensuous Italians, look at the fierce Bedos who became the obese Saudis etc.
In Sicily they'd arrived via Normandy and were already Franked up a bit -- they had a two king dynasty I think, both named Roger. And the elder Roger wanted a well-rounded education, so he hired (egad!) an Arab tutor. Later on they drove the muzzies out of Malta -- Maltese being a Semitic tongue with a broad loan vocabulary and altered grammar (sez McWhorter).
Then there's the European-Americans who became the queer Anderson Coopers and David Hoggs. They were extinct in two generations.