Well this would be step one to try to motivate some US company to start manufacturing. Then once it ramps up they can step in with banning existing stuff without causing too much disruption.
Though the US should probably just learn from China: Does DJI want to sell in the US? Setup a 50-50 JV with domestic production, skill and technology transfers, or go away.
I wouldn't read too much into the national security justification. It's a political argument to an economic policy.
Have you seen what's been happening in Ukraine? OTC drones are critical military equipment now.
Not having a domestic drone industry is like not having a domestic rifle industry, you cannot have an infantry without it.
Innovation happens under competitive pressure. The US just created a domestic vacuum.