User blog comment:Isickell/Core deck case inconsistency/@comment-26147696-20190114062448

Core deck cases could have been revoked after, what, Three-Four Disasters we know of not including the "disaster" which seemed to happened like 5-6 years before the first season. The show covered around 5 years at most, there was a 18+ year gap after X to Ace.

So my guess is that Core deck cases were considered to be either unsafe/unstable, or unnecessary as they had a better system. Which could be the case as half the reason for core deck cases was the buddy skill, which is not needed in there age, while the device they are using can replace the function.

There is also the chance that the core deck case used in ten thousand years is just Gao's core deck case left to be used by the future buddy of Balle Soleil. Wait no, the one used appears identical to Gao's Neo core deck case.