The Ancient Geek
That is very one-dimensional thinking.
The cargo manifest could very well shed some light on where the aircraft may have been taken. It might shed some light on who took it, what facilities they would have required to unload and move whatever they were after.
At the very least it would shed light on whether there was actually anything worth stealing in the cargo.
Or maybe they were after a person or persons who were onboard?
Whatever, the details of the cargo manifest are certainly material to the investigation at this point, where almost nothing can be ruled out.
And not exactly onerous for the Malaysians to produce. Unless there's something they don't want us to know.