This is under the assumption that Kaito purposefully omitted information about the hangar , which I'm sure of because literally nobody knows what happened in there, but yeah I was thinking... it would not do him, nor anyone else any good for him to walk up to everyone post-trial and be like "yeah Kokichi wasn't evil and did all of this to try and save us actually" (even if he did believe it or somehow that came straight from Kokichi himself) because it just wouldn't work .
Kaito's belief can only go so far, (as in, not everyone has his affinity to place so much trust in someone, AND ALWAYS BE RIGHT, especially not in Kokichi considering the circumstances)
and nobody believed in Kokichi except for Kaito, (albeit everyone was well within their right to not have the most positive opinion of him even in death) and the only time he could do so was moments before his death . Putting aside his pride -- something he often couldn't even do for the two closest people to him -- and a long-term rivalry for this poisoned, sickly boy who was entrusting him with his life .
Kaito was his legacy; whatever happened in that hangar dies with them alone . Kokichi could've very well died afraid and in pain, but as long as Kaito had a script, and an exisal- he was this selfish, vindictive puppetmaster masquerading about the trial with little care for who gets caught in the crossfire, so long as he gets to stare down the mastermind and claim that he had won. The survivors will never Kokichi's true intentions; they're meant to take what they saw at face value. With no way to prove anything definitively there are infinitely many truths they could possibly believe in . Anything could've happened . This is what makes Kaito- the thematic embodiment of faith and trust- the one to carry out his plan so significant.
In my opinion, for him to go into explicit detail about what was said and done in the hangar- to relay the full truth- would be to dishonor Kokichi . Whatever happened in the hangar, if they had spent their final days alive there fighting, talking, or maybe even just being honest and vulnerable, nobody needed to know .
But I also think about Kaito's internal turmoil that came with watching Kokichi devise a crime scene while slowly succumbing to poison . They're both in pain , on borrowed time -- they're just kids and it's miserable . The situation that they were in left them at their lowest after weeks of pretending that they were untouchable . Forced them to confront their mortality and their weaknesses . He has to watch the almighty Ultimate Supreme Leader struggle to even breathe . Minutes before putting him to death for a plan that he will never know was actually successful.
Kaito couldn't act heroic or offer any platitudes --there wasn't a need for that, not when Kokichi could already see right through him-- and lord knows what Kokichi "I Don't Have a Guilty Conscience" Oma felt after driving the both of them into this stalemate which lead to Kaito dragging him by an open wound on the floor . Chapter five really just put the two most emotionally unavailable people in the worst possible situation and told them to Figure It Out.
And Kaito really just . had to take all of that to his grave . Told everyone not to cry for him, send him off with one last smile !! Smiles moments before his death because he entrusts Shuichi and the people he loves to end the game, that maybe all of those hours of pain he and Kokichi endured in that hangar could actually be worth it .
Or maybe I don't have a full understanding of the guys yet *shrug*
