Am I missing something here? Why would the FDA approve it then?
The FDA rationale is explained in the last paragraph:
The FDA on Monday gave the drug “accelerated approval,” based on evidence that it can reduce a likely contributor to Alzheimer’s, rather than proof of a clear benefit against the disease.
It seems there is evidence the drug is effective against whatever this “likely contributor” to Alzheimer’s is but not evidence it is effective against Alzheimer’s itself. To me, it sounds premature (AKA “shady”) to bring the drug to market as an Alzheimer’s treatment at this point.