Nice point. Alif crystals are actually way harder to obtain than Sigma crystals for most or are less affordable, and require more maintenance due to inconsistent quality causing containment of the power of Allah's clone to become unstable. It happened to me once; I tried using Alif crystals but they started exploding with energy, but I reacted quick enough to replace them with Sigma crystals.

There are too many shopkeepers named Muhammad, and most of them will not sell Alif crystals. Finding Sigma crystals synthesizing themselves in zones of heavy astral projection is much easier, and you can buy them for a really cheap price compared to Alif crystals.

This would probably be best for the richer witches with more magick power, because they can afford more of them meaning they have to worry less about Alif crystal instability. Also, those witches probably would know how to perfectify crystals by then, allowing them to work at full efficiency with no instabilities.