Tax planning. That's what you do in Dec. Crystallize gains and losses.

Furthermore that's only one-third of his holdings. Now that we're in January earning season and the Jazz IPO are coming, he could not take any action until mid-Feb if he didn't do it in December. Same with Brewer, who sold only a small portion of his stock. And on the insider trading file, Milton also purchased 7000 new shares in December after crystallizing his gain.