My 2 cents worth. I was also holding at pudong the time this all happened.
The problem as that there was alot of planes holding and Pudong approach was being less than helpful for everyone and would not let any plane divert to any near by alternates. Typical Chinese ATC " cannot" procedures!
I believe it was at this time when ATC refused to allow any aircraft to divert to nearby ZSSS or any other nearby airport that Qatar made the choose and made there decision they were landing at ZSSS.