Noting all the economic destruction, that people suffered medical complications where many died, and that disastrous long-term effects, especially on children, are yet unknown: I suggest it’s because he fears what his powerful, incentivized accomplices (in the “private sector” and in both parties) would do to him if he spills the beans on their culpability more than he does what Rand Paul will do to him if he doesn’t. And the only thing preventing them from removing him from the board is a deadman’s switch/file that names names.
If anyone has a speculative scenario that makes more sense, feel free to share it in “Comments,” below.