Probably because (just like almost everything else) he isn’t a dictator that can unilaterally reshape a whole branch of government. Congress sets the number, not the President. If you want to actually see reforms go out and vote in more Representatives and Senators.
I am so sick of seeing this argument. SCOTUS didn’t give him any more actual powers, they shielded him from prosecution. He can’t just unilaterally declare he’s dissolving a whole branch of government, because he never had that power in the first place. What do you expect him to do to actually back that up? March the army in?