I sometimes wonder if the answer is: we put a higher value on human life.

Preventing mistakes and accidental deaths is not trivial in a factory and especially not with ship building. Often doing something with very high safely means doing it more slowly and in a more costly way.

That could change with automation but it may also go the other way. For example which factory will build things more quickly, one that allows humans to work next to powerful robot arms, or one that takes the safe approach?