My father was an expert on the assassination. I grew up with the Warren Report strewn on our kitchen table. He covered Ruby’s trial for the Saturday Evening Post and was working on a book about Ruby when he died. He interviewed every single player...and his conclusion was the same as yours: Too many people would have had to keep quiet..and that’s just not human nature.
I agree with your dad, Oswald was the lone assassin and there was no conspiracy. Oswald was too much of a loner. Over the years I’ve read many books and articles about the assassination. It’s an interesting pattern that those who really knew LHO have no doubt that he killed Kennedy and that he acted alone.
Not so many people knew of the conspiracy. Several people introduced different theories mucking up the picture.
Most people got tired of multiple theories and don't care anymore.
Some witnesses died early on
Many are gone now 45 years later.
Easy to go back to basics and simple story (foccault's razor?).