Most scholars suggest that the family needed to remain secret so that they would not fall prey to maurading bands of local Arabs.
Hugh Nibley
"One illuminating 'aside' by Nephi explains everything. It was only after they reached the seashore, he says, that his people were able to make fires without danger…That tells all. 'I well remember,' writes Bertram Thomas, 'taking part in a discussion upon the unhealthfulness (danger) of campfires by night; we discontinued them forthwith in spite of the bitter cold.' Major Cheesman's guide would not even let him light a tiny lamp in order to jot down star readings, and they never dared build a fire on the open plain where it 'would attract the attention of a prowling raiding party over long distances and invite a night attack.' Once in a while in a favorably sheltered depression 'we dared to build a fire that could not be seen from a high spot,' writes Raswin. That is, fires are not absolutely out of the question, but rare and risky—not much fire, was Lehi's rule. And fires in the daytime are almost as risky as a night: Palgrave tells how his party were forced, 'lest the smoke of our fire should give notice to some distant rover, to content ourselves with dry dates,' instead of cooked food.
"…All this bears out the conviction, supported both by modern experience and the evidence of archaeology, that Lehi was moving through a dangerous world." (Lehi in the Desert and The World of the Jaredites, pp. 72-3)