If the black box pings go down the drain, the conclusion for a south path from the sat pings might follow. After the release of the (incomplete and edited) raw data there is still no evidence, why only a southern path is possible.
There was and is no need to protect this evidence and the methods, how this conclusion for a southern path was reached.
Nobody has come up for a valid motive to choose a southern path, and discussions about a possible northern path have been avoided.
To repeat myself, if it wasn't some kind of a weird accident, the motive will lead to evidence.
edit:
henra
In an investigation it is of utmost importance to keep an open mind.
Wise words. Doesn't that include the option, that not only an accident but also some kind of criminal action may have caused the disapearance of MH370?