Let's refresh everyone's memory.

Chevron won Chevron v. Natural Resource Defense Council. The case focused on what was meant by a 'source' of pollution as used in the Clean Air Act of 1963. The EPA was on the side of Chevron, and NRDC sued in the hopes that the court would interpret the law as they, rather than the EPA, interpreted it. The court deferred to the EPA.

So while you think you might want deference to the agency, sometimes it's nice to have a judge.