How do you know? Do you have proof that Islam is just following arabic traditions? Or is it just an assertion? Have you actually looked at the conditions of pre-Islamic arabia?
If Islam was so similar to pre existing arab traditions, why was it considered a huge social and cultural reform?
You would say the same thing if God made His final messenger from among the frenchmen, or the persians, or the indians, or the russians, or whoever. Just because the message originated there does not mean we are suddenly following arabs. I would follow the Prophet Muhammad even if he came from a group of people whom for some reason I hated.