The main reason that made Asian spices so expensive as trade goods for Europeans was that they were only produced in a few places and took a long time to get to Europe. Spices like pepper, cloves, nutmeg, and cinnamon were primarily sourced from specific regions in Asia, particularly the Moluccas (Spice Islands) and other parts of Southeast Asia. The long and complex trade routes, often involving multiple middlemen, added to the cost of these spices by the time they reached European markets. Moreover, the high demand for these spices in Europe, used for preserving food, flavoring, and even in medicine, further inflated their prices.
The other options presented do not accurately reflect the historical context of spice trade as significantly as the limited production locations and lengthy transportation times.