Answer:
-to correct past mistakes
-to gain federal funding for city planning efforts
Explanation:
City planning doesn't necessarily has anything to do with federal requirements, cooperation between governments, or even renewable energy. The Federal Government in the US specifically has no such requirements, and it is the same for many other governments. Renewable energy is used in planned and unplanned cities. And cooperation is also unrelated to that.
What can actually happen, though, is an incentive from the Federal Government depending on what is being planned. Also, the funds used in a planned city usually result in less costs and better functionality anyways. Besides that, you can always see the problems that unplanned cities have and avoid committing the same mistakes.
