There are only a couple of possible conclusions...
Ochi, also known as Ochi of Bestoon, was a humanoid alien male who was
a Sith loyalist serving under the resurrected Dark Lord of the Sith
and Galactic Emperor Darth Sidious during the New Republic Era.
Sometime after 15 ABY, he was sent to retrieve the granddaughter of
Darth Sidious—Rey—from her parents. Ochi killed both of them when they
refused to give him Rey's location. Sometime later, he was tracked
down by Luke Skywalker and Lando Calrissian to Pasaana, where Ochi
became stranded and eventually died.
Ochi was an assassin and Sith Loyalist who was assigned to find Rey and bring her back to Darth Sidious when she was a child. The Passanna plot in film allowed Rey to find Ochi's dagger and we may assume that this is HOW Ochi would find his way to Sidious/Exogal, meaning that he needed the dagger in order to find one of the Wayfinders (Sith Holocrons) to actually get to Exogal.
So the set-up with the Sith Dagger seems to rely on time and/or religion, as we may also assume with the aid of the Star Wars Visual Dictionary that The Sith Loyalists and/or Sith Eternal would of been responsible for creating such a limited device that, in theory, would become useless, should the wreckage naturally erode or plunge further into the sea.
This could be about either believing in a time window being spiritually important to their plan or simply a way to protect the Wayfinder/Sidious, as it was not the only one and therefor not the only way to find Exogal, and perhaps they didn't want it to be exposed out there for too long, for just anyone to find?
The Sith Eternal was an organization of cultists loyal to the Sith
religion who continued the Sith belief and sought to resurrect its
tradition. The Sith Eternal were followers of the Dark Lord of the
Sith and Emperor, the Sith Lord Darth Sidious...
However, while there is not much yet known about The Sith Loyalist, or more importantly, the cultists: the Sith Eternal, it might be possible that the Death Star wreckage might defy physics due to some members of cult using the Force to keep it in place.
It has begun to come to light that some of the Sith Loyalists, Sith Eternal (Sith cultist), or Alchemist like Albrekh may have been dabbling in the dark side of the Force. Even the Knights of Wren have been revealed to be "mildly" Force sensitive, let a lone we don't know what The Sith (spirits) or Palpatine was also able to do. So this might be one possibility.