I don't think that houserule adds anything to the game.They very much could have picked the lock. Once they rolled and failed, that lock was revealed to be unpickable.
But if they had succeeded they would have picked the lock, thus revealing it to be a pickable lock.
Call it schrodingers lock if you will
I hated that the rule existed in 3e, it both doesn't make sense to me and feels too gamey (and punitive).
Is the lock now unpickable by everyone? What if a more skilled character attempts to do it? What if the Cleric casts Guidance increasing the character's skill?
What if a previous adventurer had once tried to pick the lock? Is the lock forever unpickable?