That's an excellent question. The answer I would give is that the process by which the Norse settled Greenland did not actually ultimately work out in the first place. Colonization isn't a simple matter of gathering enough people to form a colonizing party, staking out an empty(-ish) piece of land, and building a new settlement there. Once that settlement is built, there needs to be a steady stream of consumable goods being provided, and until the new settlement can produce or trade for those goods on its own right, the colonizers are effectively subsidizing that settlement.
The settlements in Greenland never really reached that point. The leading hypothesis at this point for why Greenland collapsed was that the Arctic trade routes dropped far-off Greenland from their destinations--and without that trade, the settlements couldn't sustain themselves and collapsed. Newfoundland may be a more hospitable place than Greenland, but from a trade situation, it's even worse: it's not offering any trade goods to Europeans that Greenland or Iceland could be providing (at much shorter journeys), but it's still probably not able to tap into the North American trade network--I think you have to make it to Nova Scotia or New Brunswick to do that.
Stories of Norse Greenlanders visiting Iceland mention their poverty. They would come to Iceland and taste beer and bread for the first time in their lives. They lived, yes, but they definitely did not thrive over there. Perhaps they were sustainable, but they were on the very edge of being so, and when conditions worsened (worse climate, lost trade routes, competition, etc.), they weren’t any more and these settlements were abandoned.
The Norse mostly settled Greenland because they had to, not because it was such a great place to be. It was a frontier, settled by desperate people. Leif's father, the chieftain Eric the Red, had moved there because he had been banished from Iceland over a murder.
And of course the Greenland colony wasn't really sustainable, which is why it died out when a couple of hard turns came their way (climate change and getting cut off from trade for a few years).
