If one only more GOP senator flips, the FCC's Net Neutrality order will be up for grabs

Federal agencies may report to the president, but they are created by and get their rule-making power from Congress.

Most likely it is just my non-lawyer dense-ness showing, but if Congress have the power to grant itself the authority to review regulations, why doesn’t it already have the authority to review regulations regardless? Is there a legal reason they can’t do so, but can grant themselves the power to do so?