Sure.
If I understand your question correctly, some of the major projects that have been proposed have taken years and years to move through the various permitting and processing. Sometimes the projects are abandoned because the economic fundamentals change over time, and so on.
This is to provide some certainty to proponents of projects all across the country—always doing adequate environmental assessments, but making sure there's one review for each project, no duplication, and time limits for the projects to help provide certainty to the proponents.