A long time before the series, long enough for it to be forgotten ancient history, there used to be a lot more Un-Sorcerors; they were probably even the norm. At some point, after enough magic-users were born, a war broke out between normal humans and sorcerors, which the Muggles lost horribly. At some point towards the end of the war, Delphine was hastily slapped together for some sort of desperate suicide mission. It's not just that Un-Sorceror's can't control it; it has a lock on the controls that actively shuts out any sorceror from using it, to prevent it being used by the 'enemy' should the pilot fail. In order to stop it [since, as we know, the thing's hella agile], the sorcerors of the time encased it in quartz and the pilot suffocated.
The sorcerors won the war and the un-sorcerors were pretty much wiped out. The few survivors interbred with the sorcerors, which is why abberations like Rygart show up on rare occasion.