Because the people in charge had the equivalent of many degrees in socialism, communism, and Marxism – they had written multiple books on the subject, participated in numerous conferences and lectures, and had spent most of their adult lives practicing and honing these philosophies. Lenin and Stalin believed wholeheartedly they were implementing communism throughout their entire lives and stated so multiple times. So why not call it communism?
It’s not perfect and especially a huge amount of rockets can overwhelm it. Also it’s much more effective on slower homemade rockets, not the faster kind Iran typically sells Hamas.