Vaccine adverse reactions are treated as random 'lottery chance' events, not as reactions with an underlying biological mechanism.
Given that it is not random, it has some biological basis, wouldn't it behoove manufacturers and regulatory agencies to at least find out what's going on? At the very least to minimize risk, much as the NTSB has done with plane crashes to make air travel safer over time.
Merely calling adverse events 'rare' (which still leaves a significant injured population) or speaking in terms of overall risk-benefit is of dubious value for the individual. AEs exist, and even this has been contentious, though supporters will maintain that the medical/scientific community has always been fair towards AEs and has long acknowledged them. Establishing this, which has been itself an uphill battle motivates the next questions; how common is it, and what are the risk factors?
Treating AEs as an explainable biological phenomenon rather than a random lottery chance event takes us into a much more productive regime. We begin to discuss risk minimization through design choices or clinical stratification, we can actually begin to understand what happens in conditions like PACVS.
Until it's acknowledged and treated as explainable, there's no way forward. When approached with genuine curiosity, and a desire to find out, it is a tractable, though still complex, problem.