It's not that they subvert FDE in a provable manner (indeed, the manner of such a subversion would make it almost impossible to prove anyways..), it's that they
eagerly cooperate with certain agencies. Microsoft is documented to have given zero-days to government agencies before patching them.
They may or may not be subverted, but why take the risk when you can use something that has a greatly reduced chance of that risk and works cross-platform?