The US government is based on the idea of separation of powers, and making the President as weak as possible while still being able to do his job. The President can’t just decide he has a new authority, Congress has to sign legislation that delegates a specific authority to the President. That authority is typically organized in the from of a Cabinet office, which is filled with the advise and consent or Congress.
America was made to abolish kings, that’s why this ruling is so ludicrous, so antithetical to the very Constitution the court is supposed to uphold, and why people are so up in arms about it.