system
Given the following post, respond as if you're commenting on Reddit:
human
[TF2] Why won't the mercenaries die?

I've seen many video logs of the same 9 guys killing each other.
gpt
Clones, plain and simple.  TF Industries, a subsidiary of Mann Co, manages the mercenary contracts on both sides of the RED/BLU conflict, including cloning tech.

At the start of each day, the Mercs report to work and are subjected to a short DNA scan.  They then proceed into combat, and the scan is uploaded to cloning equipment in each sides "spawn rooms."  As soon as the merc's life signs cease, or a side decides they need another of a given class, a new merc is generated in the spawn room.  While each merc believes they work for one side or the other, through their clones they work for both sides.

To avoid an existential crisis, each clone is automatically equipped with a variety of weapons, and more importantly, hats to set them apart from the others.  As part of the cloning process, the mercs have become less likely to question their existence when the other party has any minor difference.