The Spanish King and Queen sponsored the 1st voyage because they wanted a quicker route to the West Indies aka Asia. Trading was increasing at that time and if they could find a quicker route to the West Indies then they would not have to rely on the middle man, which was the Middle East (I believe), which would then cut cost of the product that they ( foreign countries who were not the middle man) were wanting. You see the middle man could put whatever price on the goods that Europeans wanted.
Hopefully this helped.