Silk traders primarily used land-based trade routes more than sea routes due to several factors, but the most compelling reason among the given options is:
Sea routes were too dangerous to use for luxury goods.
This answer reflects the challenges posed by piracy, storms, and other maritime hazards that made overland routes safer for transporting high-value items like silk. While the other reasons may have some validity, the safety and reliability of land routes played a significant role in the trade of luxury goods during that period.