The filmmakers could’ve given Luke a different motivation for staying on Ahch-To, while not having him be out-of-character, contradictory to his already-established character traits (like redeeming other family members; seriously, if Luke redeemed Anakin in Return of the Jedi, why wouldn’t he redeem Ben?) or undoing his arc from the original trilogy so they can re-do that arc all over again. I mean, why would he be looking for the first Jedi temple, as mentioned by Han in The Force Awakens?