Would this be better interpreted as "why has he come back" or "remind me why he's here"?
Can you also say למה הוא פה שוב and have it mean why is he here again? Or is that bad Hebrew?
ll עוד means 'more' or 'still', שוב mean 'again'. So,
Why is he here again = למה הוא שוב פה
Why is he still here = למה הוא עוד פה
You can use עוד פעם (literally "another time") instead of שוב though.