Because they don't want people to know that a commie did it.
Oswald was CIA from start to finish—and the designated patsy.
He was sent to Russia as a low level counter-intelligence agent along with several other folks.
Their handler was James Jesus Angleton.
We have the old CIA files—no need to debate anymore:
https://www.amazon.com/Oswald-CIA-John-Newman/dp/0786701315
Yep, to sow confusion and deflect blame from the left. And on top of that they blamed the right with their “climate of hate” theme.