I don't think it's a question of him not wanting to "take chances" -- the point is, the most important thing he can do to sustain and even increase his personal wealth is to do his job correctly. That should have the side effect of lots of other people ALSO sustaining and even increasing their wealth. But if he were actively pursuing individual market opportunities for himself, it would be easy to show that he's not doing his job; the downside risk of him not doing his job is WAY MORE than the potential to make a few bucks shorting UAL.
Putting your money into t-bills and money markets says "I don't trade the markets" and that's a very important statement for him to make.