You're looking at it completely backwards. Congress was fine to let the EPA run around and do whatever, because that means people can bitch at the EPA instead of Congress.

> Why is it the court's job to tell congress what they meant to say?

That's... not what they're doing. The court is telling Congress that if you want an agency to have the power to make vast, sweeping changes, then you have to be explicit. They don't get to create an agency and then just give them blanket authority to do anything they want, at any scale.

It is the court's job to ensure the law is enforced as written. Where ambiguity exists, it is the court's job to interpret the law. That's literally the entire purpose of a court.

Congress is not mute. Congress speaks by passing laws. Any other, less formal means of speaking is the voice of members of Congress, not Congress as a whole.

>It is the court's job to ensure the law is enforced as written.

The supreme court has no enforcement mechanism. It has no army, no police. Abiding by Supreme Court rulings is by tradition only.

>Where ambiguity exists, it is the court's job to interpret the law. That's literally the entire purpose of a court.

This is also by tradition only. The Constitution doesn't specify this, nor are there any laws that say this is the job of the court.