Originally Posted by doodlebug
First and foremost, because that is what Allah (swt) wills, and only He can know why. But we do believe that Allah (swt) decided to stop bringing revelation through Bani Israel (the Jews) because they disobeyed the prophets so often. And according to the Bible, Allah (swt) also promised the Ishmaelites a great nation.
I hope that answers your question at least a bit.