Nice to see you posting. A good question that can only have meaning to a PWP.
We did try to deal with this question at one time (i think). I think what we came down to is the unexpected "plasticity" of the remaining nigal neurons and their interplay with what other neurons that can be integrated into the dopaminergic system; such as the "hijacking of olfactory neurons to become dopamine producing and /or storing and relaying "helper cells".
I never had the shakes very bad, but get them off and on now. I don't think we'll ever know the answer to this question in our lifetime. We can speculate, but untill the actual documentation of ,what is commonly refered to as "Shaking PD" dominant symptome into "hypoactive" PD type, and even back again. I think that most of us have probably noticed a decrease or an increase of specific PD symptoms. Can't say why. cs