1. At high latitudes, the circumference of the Earth isn't that large. But that's only a bit of the story
2. Europeans weren't white when Greenland was first settled, I think. I don't know the exact timeline, but google says that the genes for whiteness first emerged about 14K years ago, and ChatGPT says that white skin among Europeans became widespread and prevalent about 5000 years ago, definitely after Greenland was settled.
3. Migration to Greenland could occur by foot during ice ages. Pretty sure Europeans would have to take boats.
4. The island was settled way, way before the Vikings were even in the picture.
5. Greenland probably didn't offer much to the Vikings. Even during the medieval warming period, there were no trees. And without trees, there are no boats and houses/shelters are hard to make.