The qualities that make him Superman are internal, not external. He doesn't need them to physically be around to keep him grounded, they did an excellent job raising him and now he's a man who can take care of himself and any challenges life throws at him. THAT's Superman, and needing parents to keep him grounded is not a quality he should have IMO. It makes him seem like a weak willed tyrant in the making, not the first among superheroes.
That goes for Lois too, though she's a little more complicated. She's incredibly important to him for a multitude of reasons, but he's a fully formed person without her ,she doesn't need to ground him. Nor would she want to be needed for such a thing.