Government is going to target journalists regardless of the ethics and legality of it. Joining a profession with less access to vital government secrets and more scrutiny by government than any other seems like an odd choice for a spy.
An example: a "office building" that has a large underground lab. Normal people see a construction site with a few dump trucks of dirt leaving. A spy will watch long enough to figure out it isn't just a few dump trucks, a lot more dirt is leaving than should be. A journalist has cover to watch long enough.
It is a double edge sword. A spy who can copy the real blueprints, or works in the lab is better. However the people who have that access to that might not talk at any price so you take what you can get.