I think it's important to remember that Columbus was funded by the Queen of Spain, so it wasn't all private efforts. The kingdoms and the city states of 15th c

I think it's important to remember that Columbus was funded by the Queen of Spain, so it wasn't all private efforts. The kingdoms and the city states of 15th century Europe were like competing family owned businesses (large property owning and managing businesses). The two keys for building a scalable success are competition and the profit motive. By definition, profitable means you get out more resources than you get in. Thus anything that is scalable must be profitable. The Chinese ran the missions for reasons of glory, so they did not concentrate on profit. As a result, the missions did not scale and were cut back when new rulers came to power. The same goes for NASA. But the monarchs of Europe were trying to make a profit so their exploration strategy was far different and far more cost effective.