In modern times this is known as plagarism
The Arabs at the time of Muhammad had a sense of being "left out" of communication with God, a realization that a prophet had never come to them as did the other "people of the Book".
But by the time that the Koran had been put in writing by Muhammad's historians and followers, they had all come in full contact with Jewish and Christian cultures - Syrian, Abyssinian, and Egyptian Christians and Hebrews from the North and East.
What I never understood is that even with the ability to take from so many direct sources, the Koran still has the basic timelines of the Old Testament all screwed up. Although I have great respect for Muhammad's search for God, I could never accept the Koran as Divine because of it's many contradictions. The only way around them is to claim that it is the Bible, Jews and Christians who have it all wrong.