I just realized something. Years back I read that the diversity of sects and movements increases the closer you get to the "center" of the Muslim world. Here you can see a map of Sunni-Shia distribution. Note that at the antipodes there seem to be few Shia. In fact, the frequency of Sunnis seems to be >99% in the Maghreb (Morocco, Algeria and Tunisia), while almost all Indonesian and Malaysian Muslims are at least nominally Shafi Sunnis. As you move toward the heart of the Muslim world, there is an increase in the percentage of Shia and a proliferation of movements hard to put into a box [1].

This me struck as rather similar to the pattern you see when you have a far flung population that spreads from an initial region of habitation, that is, the highest diversity of lineages is found at the origin. This is the result of neutral mutations accumulating in a region where a lineage has been present for many generations (while regions colonized later have a subset of the original diversity, that is, they go through a founder effect or a bottleneck). The implication from analogy is that the diversity of Muslim groups in the center is not the result of local conditions as much as the reality that more time has accrued to establish heresy than in the periphery. I could be wrong, and can think of many counter-arguments, but I thought the idea was weird enough to throw out.... (it jives with my conception of religious dogmas and creeds as being randon coalitional markers that emerge periodically from the minds of rational thinkers "gone wild." Now and then theyt stick for whatever reason)

Hell, we know that baby name frequencies float like randomly as if in genetic drift.

Minor addendum: Note that I am suggestiong a mutational random genetic drift model for creeds and mantras and what not, not the basics of religious experience which I think are pretty universal and constrained by practicality and evolution. The reply would be that creeds and mantras have strong functional roles.

[1] For those who want specifics, for example: the Ibadis dominate Oman, a splinter group from the Khajirites. The Zaydis are prominent in Yemen, who rest at an equilibrium between Sunni & Shia. In Saudi Arabia you have a Salafi elite and an oppressed Shia minority in the east. In Iraq, you have a split between Sunni and Shia. In Syria, you have an Alawite minority whose Muslim status is in dispute. In Turkey you have the Alevis who are similar to Alawites. In Lebanon and its environs you have the Druze, who are even more peculiar than Alawites. Not that there aren't deviant movements in other parts of the Muslim world, but, I sense that the further you get from Mecca, the less likely this seems to be....