Quote Originally Posted by lololink View Post
Ultima Weapon traps the primals and prevents them from being summoned again.

Same goes for the seal from mor dhona and Dalamud trapping Bahamut, all Allagan techs were aimed so that primals couldn't be summoned again.
Ultima Weapon simply consumed the primal that was summoned. We weren't expressly told that the Ixal, Amal'jaa and Kobolds were unable to summon again during that time. If that were the case then we would not have been able to summon the egis prior to Ultima Weapon's destruction either as they draw on the very same aether the primals are constructed from.

The seal in Silvertear Lake was something else entirely as it prevented summoning as a whole, including primals like King Moggle Mog who had never been summoned before. One of the persistent theories is that the seal simply sealed off enough ambient aether that there was not enough to actually summon anything. The original 1.0 cinematic showed the primals escaping the lake, yes, but a lot of 1.0 content was retconned and the introduction of primals like Moggle Mog and Shiva threw a wrench in the works there as neither of them had ever been summoned prior to our encounters with them so they were not sealed in that lake. The whole 'myth made manifest' thing makes it incredibly unlikely Silvertear Lake actually held the primals themselves but rather just a catalyst needed to create and summon them.