What is the most important reason why European merchants began searching for sea routes to Asia in 1400?

What is the most important reason why English, French, Portuguese, and Spanish merchants began searching for sea routes to Asia in 1400?

Trade.

Europe had been trading (importing / exporting goods) with Asia for centuries, but it was very expensive and time consuming to transport goods by overland caravan, so they needed to find oceanic routes. The sea routes between Europe and Asia allowed imports from Asia at a fraction of the cost and in far greater volume.

~ Pax