Rephrasing:
It only takes a handful of those connected to the assassination who held material knowledge of the events died within a few years of the assassination to have been killed for the probability of a cover-up, implying a conspiracy, become extremely high.
If, out of a group of 50 people, 5 of them win the lottery in the same year, you can conclude that it is almost certain, beyond reasonable doubt, there is foul play. The fact that the other 45 do not win, does not alter this.
Considering the witnesses who did not die, one can assume that it was not necessary for them to be to killed. If all witnesses were, suspicions would be overwhelming and the scheme would collapse.
Mathematical consideration of probabilities prevents us jumping to conclusions – Just because something "feels" true doesn't mean it is. Probability helps us weigh different explanations and decide which is most likely, objectively. When we use logic, we rely on facts and structured arguments. This helps avoid emotional thinking and keeps discussions focused on evidence. This is how, for example and NTSB investigation would be run, where finding probable cause is crucial to future safety.