The simple answer is that the obsession with goons and fighting during the 1980s and 1990s pushed out many smaller skill players who should have been in the league on merit, but were instead replaced by AHL and ECHL-level knuckle-draggers.
Moreover, thanks to Alan Eagleson,+ NHL wages were seriously suppressed in the 1980s. So if you were a guy like Lavallee who was getting screwed around and kicked around from team to team, it was a lot easier to go to Italy or Switzerland and make more money living in a beautiful city and basically say 'f*** the NHL'. Guys like Dan Hodgson and JF Sauve did basically the same thing.