Yeah, the most probable culprit is Kellhus himself. If the Consult couldn't find it in 2000 years, I have doubts they'd find it in 20.
Why he would have destroyed it is a whole different issue. To deny Akka questioning the ones left there? Then why let Akka find the map? Then again, it could be something deeper, like Kellhus setting up what Akka will find. Could all be drawing out what Seswatha is guiding Akka towards...