I respect Hawking and all he has learned, and his contributions to society. But, I also believe sometimes a person can get so close to the trees they no longer can see the forest too.
I have no knowledge of why he reached that conclusion. Is it strictly science based or is some personal experiences at play too? I would hope both considerations are at work in his conclusion, but i just don't know.
He was a very courageous, intelligent and well learned man who contributed much to society where many people in his shoes would have given up. I am inspired and grateful to him for that. I do however, not agree with his conclusions on heaven.