“Lyndon Johnson was white trash”
No doubt there. But high-level involvement in the assassination of JFK wouldn`t have survived all these years without someone blowing the lid open. Even Watergate`s “Deep Throat” came out before he passed on.
No one was killed in Watergate.
Higher stakes make for tighter lips.
Recall, Mob interests in Cuba were lost when someone called off air support for the Bay of Pigs invasion. Millions in nightclub action were lost to the Communists' regime as well as smuggling opportunities.
There were plenty of reasons for people to keep their mouths shut, and an accident here, a suicide there, an unfortunate plane crash, all add up over time. People 'in the know' might even have died of old age.