Apparently not, or Trump would have done it earlier, too.

There were investigations into just what reclassification would mean for other regulations, laws and treaties. These were begun during the Biden administration and are now being finished. If you just say "weed's schedule III now", without any other modifications to policy, you'll have confusion over just what that means to a bunch of different federal, state, and local agencies.

Also, you don't want a President just doing things with the stroke of a pen. Actually, that's our biggest problem right now, letting an autocrat piss all over separation of powers as a treat.