The Vikings were essentially criminal thugs. They sailed for plunder, to rob from people who worked land, not to explore or develop land to create wealth. That's why they weren't good colonisers.
While that is true for "vikings" not every Norse sailor or Norseman was a "viking" they may have gone on ships frequently and traveled alot, but the only real "vikings' in modern context would be the Pagan raiders who would attempt to sack and rob. The Greenlanders were mostly Christian and had not gone "viking" much because of the sheer distance to anyone worth raiding. The Greenlanders were alright colonizers, and if there was any reason that made it worth facing the Skraeling threat they probably would have stayed. Infact it was said many of them thought that in a few years they would try to colonize vinland again, and just like the United States space Program eventually interest died off.
Albeit let's say a contagion from Greenland spread to the Natives in the short time the Norse had traded and lived peacefully with the Natives (maybe even the Plague that killed Erik the Red OTL) and killed off three quarters of the population, Thorfinn's colony would have lasted longer and a subsequent die-off of Natives would make the continent ripe for colonization.