There were several shareholders' actions against the corporate officers responsible for inflating IPOs, against financial advisors for touting some over inflated issues and changes in the law (eg: Sarbanes-Oxley Act). The dive shown in your graph was induced by hype, betting on dot coms to do miraculous things (like the tulip hype in the Europe of 17th Century)--but, ony a few were unlawful. It was an emotional wave financed by debt and fueled by public irrational greed and wishful anticipation.
While I do not disagree with your take, much of the same can be said about Enron. If the dotcoms were gone over with a fine tooth comb like Enron, I'm sure you would find quite the same actions and practices. Those however, could not be construed as "oil companies".