There is always a lot of fat in these giant companies. Salaries and jobs are not owed, even if the company makes a quadrillion dollars of profit and the CEO's salary is so absurdly big that he bought a mile long yacht (CEOs are over paid, I grant you this).
So when times are harder some layoffs are bound to happen, and in all honesty a place like 343 that has not been able to deliver for almost 15 years now should have been let go a long time ago. 10 000 people working on office? That's nuts. Etc. Then there are slackers, those that have borderline useless jobs, or work on things that are bound to fail, so on and so forth.
People move on and find something else to do with their lives
, and at a place like MS they will probably be given a decent severance package that will give them a chance to turn around.