One of the reasons (which has been partially alluded to above) is that during the Great Recession, the Energy Industry was the only one really booming. Now, oil is a game where much more then just the big oil copamies are effected, unlike say the aviation industry. One of the biggest increase in U.S Manufacturing has been in machinary which is related to Oilfields and Oil and gas services. When times were good, then you has companys making news digs and prospecting and that meant that more and more equipment was being made for new fields and present equipment was wearing out faster (due to use) which mean more spares and maintenance monies. With the downturn in that, that market has taken a huge hit.There was and is also a huge market which services the oil industry from providing trucks, on site security, infrastructure, accomodation etc etc and they have taken a similar hit.
Lower oil prices take some time to take effect because oil stocks are typically bought months in advance. At the same time lower oil orices are not necessarily a boon to your electric company.Generation costs are only a part of your electric bill; you also have to add trasmission and distribution costs, which may actually go up, line losses and other charges.