Hi there, the question you're asking rests on a bit of a false premise (as you yourself note, in fact). The voyage to the Americas really wasn't about any shipbuilding technique that was unique to the 15th century; Norse ships had made the voyage much earlier, although you're also correct that their route to Newfoundland was somewhat shorter than Columbus' route to the Caribbean. (I wrote previously about Columbus' ships here.)

Anyhow, the main driving factor for exploration in the Age of Discovery was not technological, but rather social. What allowed Columbus to voyage west (and Portuguese sailors to voyage around Africa into the Indian Ocean and the Far East) was the confluence of relative political stability in their countries, interest in opening trade routes with the rest of the world, and the availability of investment capital to finance such voyages. Keep in mind that Ferdinand and Isabella were able to finance Columbus because Granada had finally fallen and they were able to turn their attention outward. It also helped that Columbus could estimate the distance to what he thought was Asia, even if his estimate was based on wildly inaccurate data.