The two basic motives for Christopher Columbus to find a shorter and more efficient sea route to Asia were the wealth and the glory, thus the personal gains of it.
Of course, the reasons why such an expedition had to take place were because of the political and economic movements in that period, where the Ottomans managed to take control of the Silk Road, and also parts of the sea routs. On top of that, even with paying taxes to them, the trade was still uncertain as it was very unsafe and there were constant attacks.
Columbus used that situation, managed to persuade the King of Castille to sponsor him, and he took on an adventure that was suppose to make him rich and famous. But, he did not find the rout to India, despite thinking that, he actually discovered totally new continents.
