I'm guessing it's because there's more to that series of side-quests than what we have now. They wouldn't let someone into their secret HQ just because he did one job for them.
Also [spoiler]kudos on there being an actual consequence for not clearing things up re: Arman.[/spoiler]
Also [spoiler]kudos on there being an actual consequence for not clearing things up re: Arman.[/spoiler]