Lack is a useful word to denote a deficiency of something, and occasionally, though less commonly, the complete absence of something. But there is a lack of so many things nowadays that the word is being pressed too much into service. For instance "there is a complete lack of spare underground wire" is not the natural way of saying "we have no spare underground wire".
Dearth is misused in the same way. "A dearth of information exists" is better expressed "We know very little". This is a symptom of the abstract-word disease.