Interesting question - Parkinson's patients aren't great candidates for amyloid therapies because amyloid deposition doesn't seem to CAUSE Parkinson's symptoms or be associated with brain function deficits in this population. At least not consistently. Amyloid builds up in a lot of people as they age, especially if they have sleep problems, but it doesn't always mean Alzheimer's or a decline in thinking. (For examples of the disconnect between amyloid burden and brain function, see this 2019 study in PD patients)