As I listened to the last 10 minutes which featured the UFO segment, I got the strong impression that he baited Rogan with the 'people coming from space' because he wanted to switch the topic away from the JFK files. The way he talked about the JFK files was weird and disappointing. I mean, if you really want justice you don't care if those involved in the assassination are still alive, what a stupid argument! And to call Mike Pompeo a good guy...c'mon man!
I thought the JFK topic was one of the only parts of the interview where Trump seemed to be somewhat uncomfortable. As to why he didn't open the files, to my mind it's pretty clear: it would have been yet another battle among thousands that he had to fight against the Deep State ("his people") and he chose not to do it. Plus, if he saw Israeli involvement in the files, that would be another reason not to go public with it, no matter how Trump personally feels about this. And to withhold the files probably was a good decision, given that it wouldn't have changed anything really at that point in time. Timing is crucial for such things. Maybe next time he'll do it (big maybe), and maybe the cultural moment will be ripe for it. But I don't blame him for choosing his battles.