I think the impetus has been to respond to stakeholders. Internally, employees are the group most targeted by corporate environmental reports. The employees want to see that the company they work for is doing the right thing environmentally. Top management wants to see what is going on within the corporation in terms of the environment, including what benefits it is bringing the corporation. A range of groups outside the corporation for example, environmental groups are also increasingly asking for environmental reports, and companies find that the reports are a good way to respond to environmental criticism.
Regulators are a frequent audience.
I think the reason these reports initially came about was that many companies had a lot of pollution issues and wanted to show what they were doing about them. The reports have since evolved into a much more mainstream activity. Corporations have in the past primarily used one channel of distribution mailing the report to a variety of potentially interested stakeholders. More recently, they have turned to the Internet, which is a cost-effective distribution method that reaches new audiences. There is no requirement in the United States that environmental information be published in a report.