Between various Traders' Guild monopolies on aerial transport, sea lanes are important for the Black Market to haul its warez between disparate communities. While slow, it is very cheap, but Earth's govts cannot make too much use of it officially as it could invite the Guild's wrath. However, small scale traffic goes on mostly beneath notice from above. The below is a whole different matter altogether, as no one can guess when and where the next Deep One attack will happen. Thus, many ships never return.