As has been pointed out on this thread, a coverup in this case by the government would send shockwaves and do even more to undermine its credibility. Things like this never stop being relevant.
One of the legitimizing myths of our government is that it serves the people and is open and just. I know, I don't believe it either, but many do and that's how society functions. A gov that plans, executes, and hides the murder of its foremost figure would be seriously damaged as a legitimate institution.
That's why other govs that have past crimes do so much to distance themselves from that regime. Germany doesn't go around calling its leader Der Fuhrer (or Die Fuhrerin, as the case may be). I'm 25, this happened way before my time, yet still affects me and interests me.
I'd say you're a pretty good exception, then. I was 13 when it happened, and to this day I have never stopped being interested in the truth of it. Your explanation as to why a government would not allow its own citizens to know the truth of one of the higher-ups in the gov assasination is a good explanation, and actually, I know this. But the frustration of knowing we'll NEVER really know all the truth, details, who did what to whom, where was Johnson, why did Ruby get let in through the garage, what REALLY happened to the interview notes the police in Dallas took when they interviewed Oswald over several HOURS which mysteriously disappeared and NOBODY knows ANYTHING about them, what happened to Kennedy's BRAIN, why were there two different caskets, why wasn't Oswald even breathing fast after supposedly running down HOW MANY FLIGHTS of stairs in the Texas Depository immediately after the shots were fired at the President.........it goes on and on and we're expected to just believe whatever they tell us. Oh well, that's life for ya.