A quest that had the chance of interrupting other quests sounded really bad, what made it worse was that the reward and failure punishments were hidden. This was beginning to feel like the quest Kilo had tried to give him earlier, the only thing preventing Merlin from declining it at that very moment was that the quest wasn't given to him by the thief lord.
Instead the quest was generated after hearing about the world's lore. The quest was given to him by the world itself, meaning it wasn't influenced by an NPC's agenda.
He eventually accepted the quest, the promise of a story that was hidden from him in his previous life was more than enough temptation. But there was also the fact that it was a hidden epic quest offered to him at such a low level.