This situation is not unusual in the corporate world. Contractors -- many times temporary workers from another country -- are brought in, kept for a fixed number of months, then let go. This is all done without any clue at all as to how it's actually affecting production.
I worked at one place that was 70% contract workers. Every year, they would have to leave. No fooling around -- nobody worked a day more than a year.
With people staggered throughout the project, all coming on at different times, it was like productivity roulette. One month a team might lose somebody who wasn't such a great worker. Whew! Dodged a bullet! The next month they might lose a third of the team within 2 weeks.
I know what you're thinking; just make a chart and keep track of when folks are leaving. But replacements weren't available until there was a documented need, which couldn't happen until the vacancies appeared. Sometimes then it would take a month or two to get one.
All of this organizational cruft was created at the highest levels, where everything is always peachy. I don't think the people creating this mess were trying to do anything bad. They just couldn't see the impact of what they were doing. By the time status reports moved up through several levels of management, things were looking good. Always.
So don't feel bad. You're not alone.