A key skill for any scientist is to differentiate quality work and science that can be easily faked.
The Alzheimer's and Parkinson's fields are too easy to fake, and too difficult to replicate. The new ideas are only ~20 years old. Big pharma companies are understandably wary of published papers.
When people say "trust the science", they often refer to things like masks, and antibiotics, and vaccines. That science is hundreds of years old and have been replicated thousands of times.
TL;DR: Some science should absolutely be trusted, some shouldn't. It's not surprising that you can't make blanket statements on a superfield ranging from germ theory to cold fusion.