They were hindered by economic development and lack of enforcement, so I'd say 1. Cost, because no one would pay for it.
Answer: In the fall of ad 66 the Jews combined in revolt, expelled the Romans from Jerusalem, and overwhelmed in the pass of Beth-Horon a Roman punitive force under Gallus, the imperial legate in Syria. ... After the fall of the fortress of Jatapata, Josephus gave himself up, and the Roman forces swept the country.5 days ago
The other areas to greatly impact Japan were the regions of Korea, which was the closest culture to Japan and therefore the main point of contact between Japan and Asia. Through Korea, the major Asian religion Buddhism traveled from China to Japan and became a major influence on Japanese culture. Hope this helped :)
