Settlements such as Brattahlid were founded by the end of the 10th century. Yeah, that's early enough for Christianity to be present, but it was far from predominate. Moreover, these settlements lasted hundreds of years.
So while they weren't exactly doing great, it's not like they simply showed up and starved either.
Fair enough. . . .Testing the argument to see if I can get a useful argument out of it
When Iceland was first settled, the environment was relatively benign because they were in a warm period. They were able to grow cattle and sheep there.
The little ice age started around 1350 and I believe a visit only about a half century later found the colony abandoned. During this time, The Icelanders were able to adapt by going to fishing. At the same time, the Inuit were also able to survive through fishing and hunting wild game. Fish was not a big part of the Greenlander's diet compared to either one.
The suggestion is that the local Church remained a stopper which prevented the Greenland Vikings from changing and adapting. The church has long been known to resist change. I grant that we all are but they seem to be worse than normal.