The main reason for the European monarchs to sponsor explorations in the fifteenth century was to manage to find a way to Asia so that they can make a big profit from the riches they can bring in on the European continent.
After the Ottomans established their empire, they actually managed to gain territories that were of great strategic importance for the West Europeans, as they managed to cut them off from the silk road. Because of this, the monarchs in Western Europe invested in multiple expeditions, so that the explorer manage to find a new sea route to the Asian lands that they were trading with, in order to be able to get their hands on the expensive and very profitable Asian goods.
Apart from managing to find new waterways to Asia, the explorers managed to discover new continents and lots of new islands as well.
