Honestly I still believe that Gith do have a cure and it's just that the Gith knight we meet is an ass.

Like, how could the Gith wage war against the mindflayers for (? eons?) and not have developed a cure?? (spoiler hag)
Some random hag we meet says she could cure us, and only can't because our tadpole is protected by other magic.

It would be pretty incompetent on their part if the Gith hadn't figured out a reliable way to remove a just-inserted tadpole.