It looks like some of these larger cases take a while to prosecute. Not saying there's no favoritism here, but FYI the Enron scandal unfolded in late 2001 and the current and former CEO Lay and Skilling's trial started more than four (4!) years later in early 2006.
My memory is a little hazy, but the fast prosecution was motivated by covering up structural inefficiencies in CA energy trading created knowingly against considerable objections by politicians, that Enron abused, and not the a priori fraud of propping up their stock for dozens of quarters to be able to trade so massively in the first place.
Edit : to clarify, politicians created structural inefficiency in the California grid, in the name of deregulation, specifically Govenor Pete Wilson and California Legislature AB 1890 of 1996.
