@Nami Maybe it just hasn't come up, yet? He hasn't had a chance to talk to anyone and introduce himself, and any other way of stating their name would be unnatural dialogue.
It seems like they may run into an old friend at some point, so their name will come up.
Also, a character's personality and knowledge matter far more than their name, especially if they decide to go by a new name in the new world. If their actions are consistent, then they are still the same person, and the name they go by barely matters.
And so far, this main character seems consistent based on what we know about them before the transfer.