Fun fan theories... but the legit reason would probably be that the rings never looked for a replacement. Abin Sur always sent his energy beam out to find a suitable replacement because he knew he was dying... It wasn't an automatic thing. At least not till Johns took over in 2004. That was one of the things he added in, but before that there was always the threat that whoever killed a GL would get their hand on the ring... unless a Guardian took it in their own hands to get it back or destroy it. It didn't fly off on it's own. But yeah, since Red Son came out in 2003 so that was pre-Johns mythology.