One reason given for shortages is that many firms now rely on “Just In Time” delivery, including the big supermarkets who now have sophisticated ICT  based stock control  systems. This is a term originally associated with factory production lines where parts e.g. car exhausts are delivered just in time for fitting into the new vehicles. The main aim of J.I.T. is to have minimum, ideally zero stocks. Thus saving the associated costs. There is a brief summary of J.I.T. and its advantages and disadvantages on tutor2u, click here.