The g'mara on Eiruvin 55a, expounding "it is not in heaven...nor across the sea" (D'varim 30:12-13), says (Soncinco translation):
Raba expounded, It is not in heaven, it is not to be found with him who, because he possesses some knowledge of it, towers in his pride as high as the heavens [neither is it beyond the sea] it is not found with him who, because of some knowledge of it, is as expansive in his self-esteem as the sea.
R. Johanan expounded: It is not in heaven, it is not to be found among the arrogant; neither is it beyond the sea, it is not to be found among merchants or dealers.
Three of these cases address personal qualities -- pride, excessive self-esteem, and arrogance -- and then there are the "merchants or dealers". (A footnote explains that this is a reference to maritime trade.) What's wrong with them?
I wondered if seafarers didn't have time/ability to learn torah. Someone else at minyan this morning thought this was a reference to people who teach torah only for pay. But we're just guessing.