So what would they be trying to cover up and what makes you think this?
My guess:
1. Suspicious (and illegal) cargo was loaded with the tacit permission from the Malaysian government. Can be gold, can be tons of $$$, or it can even be nuclear fuel or biological weapons.
2. People with fake identities were on the flight, with tacit permission from the Malays. May be FBI spies, or can even be the Malay Secret Service Personnel.
Some people watch too many bad movies. Go ahead, and expand on your
movie script theory, and explain why the Chinese government would transport nuclear or biological weapons on a Malaysian civilian airliner. And if not the chinese government, then who? And where did it come from? For the record, Malaysia doesnt even have a nuclear power plant. And who brought it down and why?
Then explain what could possibly make US, British, Australian, Malaysian, Chinese over a dozen other countries' governments conspire, along with crash investigation teams, the plane manufacturer, satellite operators and what not, all to cover up whatever you think happened?