Answer:
Because they didn't believe that there are lands outside the old world, and that Earth was flat. It was unimaginable for them that someone can sail fat to west and reach any new land. That was the case because in Middle Ages believed that Earth was flat and open sea dangerous.
Explanation:
Norse legends were not seen as true because Europeans had very little knowledge of the world outside their realm. Additionally, they were afraid of Norse warriors who usually loathed and destroyed everything in front of them. People in Middle Ages were narrow minded as they didn't realized that the world was a larger place and they had lack of knowledge.
