There are two reasons for a coverup. One reason is to keep the trust of the people. When you perpetrate this kind of cover-up, it's to make sure that the citizens have faith in your military, and or leaders. We can look to a few examples like the JFK and MLK assassinations. Another cover up would be Waco. Yet another cover up would be Gary Condit. These are examples of keeping the faith types of coverups.
Then there's the other reason, The reason that you can't explain what happened, because if the truth got out it would bring down governments world wide. These coverups are the kind you see on TV. The UFO things, and the conspiracy type coverups. Things that make the X-files look like non-fiction. If it was a UFO that brought down TWA 800, there would be many questions asked of our government. The first would be, how come we didn't know about it. The next questions would be even more intrusive. How long have aliens been visiting us? Have you made a deal with them for technology. Are abductions happening, and how come you let it happen? Why are our cows being mutilated in goofy ways? How come you're grabbing up so much land, are you making room for them to live in our country too?
The main question I would ask, if it were a UFO accident, is what kind of retribution or apology can we exact upon them?
This is why if you cover it up, just to keep the faith, you're better off, than if it's to hide something more sinister.
I've now removed my tin foil hat.
A governments credibily is built up over time, and trust is earned.