Because of Heisenberg's famous uncertainty principle...
He is assuming that God is as limited as man is, just because something is uncertain to US, doesn't make it uncertain to God.
Mr Hawking has crapped out, God did not 'roll the dice' but he does play poker. He always has the best hand and never bluffs though.
What both of these miss is the Biblical statement "In the beginning, God" is not a reference to God's beginning - but to that of us and of our Universe. I too, am often guilty of trying to ID God into the physical realm as we know it.
If Hawking is right with his "point of singularity" theory, the Universe, time, space, and all matter began from that singular point. That is enough to prove we have no concept of an existence not bound to time/space - that place where God dwells. It is so fitting that Jesus said "they know not what they do"...
Regards,
Az
Googolplex aces over?