The Vikings get a lot of credit now, but they didn't used to. That's because Columbus had better publicity. When he returned to Spain after his first voyage, he had the backing of the king and queen of Spain and he published his accounts which were widely read. The Vikings had a language which was less widely known and lived earlier in the Middle Ages when people were less literate. They also didn't leave permanent settlements. So for a lot of reasons fewer people knew about what Vikings discovered.