Final answer:
The legislation passed overwhelmingly because it was pro-environment and had strong bipartisan support, indicative of political compromises in U.S. legislative processes.
Step-by-step explanation:
The legislation requiring environmental impact statements likely passed by overwhelming majorities primarily because it was a pro-environment law and because it had strong bipartisan support.
This bipartisan support is evident as a mix of political compromises are usually made during the legislation process, as indicated by discussions surrounding command-and-control regulations written by legislators and analyzed by EPA officials. In the history of U.S. environmental laws, there is a pattern of existing firms lobbying for exemptions and a trend towards market-oriented policies for more flexible and cost-effective solutions.