Either that, or they explicitly chose those civilizations because they were incapable of making such weapons.
In theory, the Ascians could have given such toys to the Garlean Empire, but they haven't. They could have also made such deals with Ishgard under the pretenses of helping them with the war on dragons, but they didn't do that either. My opinion on this is that they haven't made such offers because they are afraid of a repeat of the Allagan Empire, the primary evidence being the situation with Bahamut. When he was released, we were given a cutscene in which an Ascian was ecstatic, saying something about how he didn't think he'd get to see Bahamut again. He then burst out into maniacal laughter. With this, and the fact that the Ascians have withheld such technologies since then, I'm given the impression that the enslavement or containment of Primals wasn't part of their master plan. It's just speculation, but I have a feeling that the Allagan's developed themselves far more than the Ascian's bargained for, and their widely successful conquest of primals actually ended up working against the Ascians until the fall of their civilization.
