During the course of many years, staff levels need to be changed. In many cases, one needs to add staff, so there is no problem, one just hires people. In some cases, one is downsizing though, and in this case, one needs to fire people. Now this of course can be the case, but, one gets a CI penalty.
In real life, a lot of the downsizing in companies is done through staff attrition: people leaving the company for another employer or retiring. There is no such thing in AWS.
I think there should be something like this: about 5% of employees leave a company per year.