At least part of the answer to this lies in the fact that the business world in today's milieu is continually changing. Markets are becoming globalized. Corporations are being merged, like IMDb.com becoming a subsidiary of Amazon.com. Financial organizations of longstanding on the brink of collapse have been bought by other financial giants, like Bear Sterns being bought by JP Morgan, with the help of the Federal Reserve. Organizations must be attuned to their own dynamics in order to keep productivity at optimal levels, and productivity depends upon job performance, and job performance to at least some degree depends upon job satisfaction. Another factor is the changing social and cultural environments in America and other Western countries.
Not only is there growing ethnic and religious diversity in the workplace there is a change in social behavior and ethics. The loss of ethics in business was recognized in the latter half of the twentieth century. In response, leading business schools, like Harvard, instituted courses in business ethics. The decay of politeness, manners and courtesy in our culture was recognized at the end of the twentieth century. Corporations hold training events for employees to school them in common civility. All these factors of business, cultural and social changes are part of the reason Organizational Behavior has become a standard part of business school programs. This is in addition to the evolving nature of business theories as they are practiced over the decades.
Business school programs have placed a greater emphasis on organizational behavior because they have realized the changing trends in companies and businesses.
Many of most successful companies right now, like Apple, for example, have transformed their work place dynamics into an atmosphere that fosters cooperation, teamwork, motiviation, and ingenuity. Apple incorporated self-organizing teams within the company, which made workers feel that they had more buy-in, or control, over their projects, which in turn increase their drive to be innovative, because the employees were more motivated to see their project succeed.
Understanding organizational behavior is definitely a necessary tool for business students or anyone who works within a large organization or has a leadership position.
Organizational behavior can be dysfunctional in ways that individual behavior is not, compounding pathology in a negative synergy. Let's take something as simple as the withholding of information in an organization. The culture of such a workplace can have a chilling effect on production or creativity in people who would otherwise be highly productive and creative, promoting paranoia and gossip that is counterproductive. It is not enough to have knowledge of the behavior and emotions of individuals because when they come together in an organization, a kind of groupthink can prevail, and this can be highly destructive to the goals of the organization. It is important to understand people as individuals, to be sure, but there is a "big picture" that management must have some insight into, as well.
I would argue that this study has become a standard component of business school programs because managing and running a business is not just about economics and marketing. It is also about making sure that the internal workings of your firm are as efficient and effective as they can possibly be. In studying organizational behavior, managers can get to be better at understanding how to get the most out of their employees. This is important today because businesses are so much more about people today. The days of time and motion study are somewhat past since you cannot promote creativity and high-quality brain work through the use of such studies. Therefore, organizational behavior is more important as a way of getting people to work well together.