Islam and the Desert

One book I've been reading lately is James Howard-Johnston's Witnesses to a World Crisis: Historians and Histories of the Middle East in the Seventh Century. The book's scope is vast and dense, and I don't aspire to take it all in until I have more time to focus on it, but here's a paragraph from pages 450-451 revisiting old ideas about Islam and the desert:

"Paradoxcially, the greatest appeal of Muhammad's monotheist message lay in its bleakness, in his clear-eyed view of a universe governed by a single divine autocrat. This made far better sense of the world in which his listeners lived than a polytheistic belief system. For local deities, even those associated with astral bodies, could not protect their votaries from nature's brute force in the desert. The affairs of men were evidently governed by some higher, impersonal irresistable force, hitherto vaguely defined as time or fate. They would live through years of plenty and years of dearth. The best among them would be distinguished by courage, powers of endurance, open-handed hospitality, generosity. But death awaited all, rich and poor alike, its coming unpredictable. There was a heroic hopelessness about life in the midst of threatening, invincible nature. Fate held away, fleeing human lives its sport. It was as if the Arabs had long been dimly aware of the overarching presence of God, but had never been able to bring him into focus before and it was Muhammad who first instilled a proper understanding of his role, no longer remote and detached, but taking a close judicial interest in the behavior of his creatures."

I see similar arguments used to explain the rise of Wahhabism in the 18th century. In the paragraph before this, Howard-Johnston references the Qur'an's lack of saints and holy men such as characterized Byzantine Christianity, and Wahhabism arose primarily as a reaction to the veneration of Muslim holy men and local animistic practices.

These are ideas about Arabian change which, as far as I can tell, hold no water whatsoever. For one thing, surely a bunch of somewhat capricious demigods do, in fact, represent a better explanation for the chances of life in the desert than a God who wishes to reward the good and punish the evil? If this is such a good explanation for the rise of Islam, why didn't Judaism, which was going through a period of proselytization, make larger inroads in the peninsula? Most importantly, why did Arabians either continue with or later return to a religious culture involving holy men and animistic practices, thus upsetting Ibn Abd al-Wahhab? I don't know why Islam spread so quickly, but this isn't it.