The Beast was an ancient monster, and it was able to decipher certain clues with the limited information presented to it. Knowing that Eos would not want to allow his secrets be known to others, Death finally acknowledged that it would not be leaving here alive.
There was a reason it feared the Temple of End, far more than it feared Eos or the Ancient Primordials, and that was because they were capable of wielding powers beyond what anyone with Origin was capable of, and if they wanted, they could erase an entity in its entirety.
For so long, Death had been feeding on the past Deaths, and he knew that this technique he was using was a small taste of what the Temple was capable of. In essence, all of these past Deaths had a slim chance of resurrection, but with this technique, they had finally been wiped out and used to feed its growth and hunger.
