The media portrayal of espionage is not in the slightest bit accurate (although, The Americans is still one of the greatest shows ever made).
In the case of this? Odds are they are just real stupid. But the intent was likely to feed documents over a long period of time. So 15k now, 20k in a few months, 10k a few months after that, etc. Because if someone is offering you a million dollars for one document? They are probably gonna hang you out to dry. If not kill you themselves.