That, and in JFK’and RFK’s cases, they were loved by millions, but their were also lots of people from all walks of life who for various reasons were pissed off at them and the Kennedy family, many with good reason, who would take out a Kennedy or two if they could get away with it. That could explain were some conspiracy theories originate from.
Unanswerable questions and unpleasant answer are the fertile ground conspiracy theories grow up in. With the Kennedys people conveniently forget that it was a pretty violent world in America, a LOT of people were getting popped, especially political figures. There was a lot of anger in the country, on both sides of pretty much every issue, and some folks were expressing their anger a bit more viscerally than the rest. And then of course the Kennedy empire was built on rum running, they had a lot of organized crime connections, and they turned against those connections when JFK was running for president, and then started trying to put them in jail.