Some stims may come from efforts of the central nervous system to jump-start the next level of maturation, growth, or development. For this reason, it is speculated, stim behavior in children who are impaired may be more exaggerated than for the child who is not impaired. The challenge is whether we can understand the underlying process. Remember, when the process is in place, learning the skill is a piece of cake. But when the process is not in place, the central nervous system compensates to find the stimulation it wants and needs.
Impairments are process breakdowns.
I think this question is close to that situation. If the child has a sensory hunger, then it needs to be fed. If it is not fed and thereby allowed to be incorporated into a more complex behavior, the child gets stuck in the developmental progression. Well then the child is not receiving the types of opportunities that encourage incorporation of movements into complex behaviors. Get that started and the self-stimulation behavior will change.