In an article on zerohedge.com (yeah, I know, but they show screen shots of the sales and the news is all over financial sites) Satya Nadella sold half his stock holdings in two chunks over November 22 and 23. This was not a pre-set sale or related to options, just a sell-off.
An appended stock chart shows that the sales depressed the MSFT stock price.
Pure speculation, but two obvious potential reasons come to mind (1) he foresees a drop in the stock price upcoming (maybe MSFT problems, or maybe general recession drop) or (2) he wants to pay the capital gains at the current rates, not the proposed higher rates.
Any other guesses?