It's not only firing, it's also taking back money already paid. Imagine the company had particularly good year, you get $LOTS_OF_MONEY, you spend it on $LUXURIES, and then next year something goes wrong, and the board decides it's your fault, and suddenly you owe $LOTS_OF_MONEY back. And you've already spent it, or invested it in some illiquid asset. Maybe very uncomfortable situation, much worse than plain firing. People aren't used to take that level of risk, so many may be reluctant, especially if other options are around.