well, the great being (srangly enough) arent pefect. remember what happened with the baterra? the couldnt shut them down, and that cost many agori and glatorian their lives, even after the war was over.as many people said before, if you were a GB, would you want the ironic defeat by your own creations?and if they can stop the sentience "virus", do you think that the GB's would be able to inject the cure or reprogram the toa and matoran while they are being shot at with xian tech and elemental powers? i don't think so. it is easier to make something that does this for them, in a more... permenant way, and buildin it before the toa, matoran, etc. come back, because if they come "infected", there is a good chance they will kill you before you can design, build, and program a failsafe attack bot