Yeah I normally hate the whole, ignorant protag. But it actually makes at least some sense here. Everyone around him is doing everything they can to keep him ignorant. And that there is a danger of him changing so heavily if his mental state changes. This is a case of let sleeping dragons lie. There is so much risk if he learns. It could go to his head, he could want to move out of the dungeon, there is just so much danger to any potential changes. And they are on a time limit, if he dies, if he decides to leave, if he grows old, or if he changes its apocalyptic. All they can do right now is by time till they figure out how to destroy the dungeon, and then figure out how to deal with him, best case he never turns on humanity, but if he does its game over.
So yeah keeping him in the dark for now is the right call. And unlike most series like this those who know are actually actively keeping him in the dark.