Zelensky just removed Zaluzhny from heading the military because Zaluzhny was getting too popular and becoming a political threat. Important to point out that Zelensky has called off the elections that should be happening right now and that there's growing dissent for his administration due to how poorly the war is going. Also worth pointing out that Zaluzhny has ties to the far right militias of the Ukrainian armed forces and flaunted this fact when Zelensky first tried to have him removed. It would be very easy for NATO to back Zaluzhny and his right wing thugs (the same ones that took part in the maidan coup) against Zelensky if Zelensky breaks with the West's wishes. US intelligence agencies are very good at pulling at threads of existing dissent to create chaos and oust difficult political leaders