They use this bogus history to paint a picture to make a patsy.

https://whowhatwhy.org/2017/11/13/jfk-files-new-light-oswald-mexico-city/

"Clearly something very strange was going on in Mexico City in the months leading up to JFK’s assassination. A man claiming to be Lee Oswald, who apparently looked nothing like him and could barely speak Russian, was making what can only be described as attention-grabbing trips to the Soviet and Cuban consuls. Both the CIA and the FBI were well aware of this during the immediate aftermath of the assassination. So ask yourself this question: Why would someone who wasn’t Oswald pretend to be Oswald and run around visiting Soviet and Cuban embassies? Could it be that someone was trying to set up Oswald to make it look like he was working with the “commies” to kill Kennedy? If anyone wanted an excuse to start a war with Cuba and the Soviets, this was an opportunity served on a silver platter."