Forced attrition plans set up the dynamic that you find yourself in a pool of peers and you know that no matter what, every year one of you is going to get let go. You don't want it to be you, you know that you can be meeting all of the objectives of the organization and still be "the guy (or gal)" because no matter what, someone is going to get picked. My assertion is that bad managers, ones who embrace behaviors that good managers do not, can find ways to protect themselves at the expense of the good managers. It isn't good for the company of course, but the dynamic is already launched into motion. Given a very small epsilon that bad (in this case unprincipled) managers are probabilistically slightly less likely to lose their jobs, the system will slowly over time select for effective, but morally ambiguous managers. This is a very common evolutionary experiment folks run in simulation all the time. The smaller the epsilon the longer it takes, but it always happens.
[1] Sometimes that leads people astray into thinking it is their organizational structure, not their people, which accounts for their success.