In other words, they already had the world-building done, scrapped the game they were going to make, and instead made a team-based shooter set in the same universe, likely with the same main characters.

On the upside, it means the game and characters end up with a lot of "history" that you can feel while playing. On the downside it means the game makes absolutely no sense at all. Though I suppose a cloning machine and lots of drugs could account for it.