Probably because every explanation you've encountered has attempted to conceal the fact that Oswald was a committed communist with high level contacts in Moscow and Havana.
Let me get this right.
We're supposed to believe Oswald, a guy who had direct high level contacts in Moscow and Havana, was then used by his Soviet bosses to assassinate the President of the United States? The Soviets would risk total destruction, nuclear war, just to kill Kennedy? You really buy that?