A sea route would have given any country a huge advantage, because Europeans desperately needed to find a new route to Asia. The disintegration of the Mongol empire made trade between Europe and Asia increasingly difficult in the beginning of the fifteenth century. The Silk Road had been the main trading route since ancient times. The price of trade goods from Asia had always been high because of the middlemen who actually transported the goods from one continent to another. Around 1400, the empire started breaking up and silk was no longer transported to Europe.
Other goods trickled in, but even their prices were extremely high. Spices were not a luxury to European nations; they were a necessity. They helped to preserve food; without them, people starved. It was believed that if European nations could find a direct trading route to China and India, more goods would be made available at better prices. And if a sea route was found, whoever got there first could negotiate to the best advantage. (They would have tried to keep the charts showing the way secret, but those trade secrets always leaked out.)