Well, that area was 200 years conquered at the time- the usual decay had not set in yet? So my guess is that there where still competent military powers around and working states & organizations. So - better to trade with these then rob a powerful enemy? The vikings where traders/mercenaries when encountering formidable opponents and robbers when they did not..

Yeah but we know they did raid Muslim areas, and furthermore, they often worked with the Byzantines who were often at war with Muslims. It could be just payment for fighting against Muslims from the Byzantines (whether indirect as booty in war or as direct payment from the Byzantines).