I used to think that way also. But after learning more about Castro, I am questioning that theory.
LBJ said he thought Castro was behind the assassination, in retaliation for the plots against him. So why didn't LBJ respond?
In any case, Castro's (and Che's) fanatical hatred of the US at at that time was near Bin Laden level (and Bin Laden wouldn't do anything to cause the US to respond, right?). I don't think there's evidence that Castro was behind Oswald's acts; but I don't think he was very rational when it came to the US. His hatred blinded him to it.
I'm sure you know this incident? On September 7, 1963 Castro visited the Brazilian Embassy in Havana to recognize the celebration of Brazilian independence. While there he singled out the AP reporter Daniel Harker (according to Harker's account) and told him this:
"If U.S. leaders are aiding terrorist plans to eliminate Cuban leaders, they themselves will not be safe. Let Kennedy and his brother Robert take care of themselves, since they too can be the victims of an attempt which will cause their death."
Castro later said that it wasn't a threat by him against JFK but a warning that if he worked with these "terrorists" that they could strike back at him. Harker later said that it was clear to him what Castro meant: he wasn't talking about the anti-Castro Cubans who would strike back but Castro.
Harker later gave more details. He said: "I never misunderstood Catro. There was absolutely no hint that he was referring to the Cuban exiles. Spanish is my first language, as a Latin- American born in Columbia, Venezuela. That'w why the AP sent me to Havana in the first place, because I was fluent in both Spanish and English.
Castro chose me for the interview because I had interviewed him two months earlier, and he was impressed with the accuracy of my account. After the September conversation, I stayed in Havana three more years and never once did he complain that I had misrepresented him. In fact, all our wire transmissions were monitored by the Castro government, which had to approve the material before it was sent out. The interview [with Castro] lasted three hours. We stood the entire time. Castro was not mad, merely colloquial. Castro remained cordial with me in the years after the interview."
This threat was published in the New Orleans paper. Did Oswald read it? I'll wager he most certainly did.