Because it works. The Vikings embodied a mindset of skaldic pragmatism: doing things because they worked, without needing to understand or optimize them.
Our bodies are Vikings. Our minds still want to know why.
I'm pretty sure the Vikings understood their craft very well. You don't become a maritime power that pillages all of Europe and reaches the New World long before Columbus without understanding how things work.
From Scandinavian countries to Malta, you only have to cabotage, but that does not mean they used the same boat in one travel, most likely they progressed from outpost to outpost, where one generation settled in one outpost and the new generation searched for new adventures abroad.
For perspective, the Roman empire imported tin from Scotland (~3500 miles/~5600km).
On the contrary, going from Norway to Iceland, then from Iceland to Greenland, and then to Vinland in a few generations is a great maritime feat.
I'm sure they did too, but its a chicken-and-egg problem: Did the Vikings build ships through trial and error and only later understand the physics behind it, or did they learn the physics first and use that knowledge to build their ships?
Our bodies are Vikings. Our minds still want to know why.