The actual reason is because a shocking amount of state business must be conducted via constitutional amendments. One example is an amendment that controls the wages of specific judges. Shit that should have been laws, or even just some sort of policy.

This was done with the specific intent of enshrining white power in Alabama's government. It gives all of the power to rich white men in the legislature. That makes it extremely difficult, if not impossible, for the majority-black regions to exercise any kind of local power.