Some of these guys aren't necessarily resigning their CEO positions, but other boards they sit on.
Example: AT&T CEO resigns from Boeings board.
www.cnbc.com/2017/12/15/randall-stephenson-chairman-and-ceo-of-att-resigns-from-boeings-board.html
With Papa Johns, John Schnatter resigns as CEO, remains as chairman of the board.
washingtonpost.com/news/business/wp/2017/12/21/papa-johns-founder-replaced-as-ceo-weeks-after-blaming-the-nfl-for-sagging-pizza-sales/?utm_term=.bb66e0225885