Based on your description, the tract seems to have been designed with very low expectations of achieving results.
Bingo!
They don't give a flying fig if anyone who is "invited" comes or not. In fact, just imagine if significant numbers of the public did come: Typically, in the US, district convention sites hold about 10-15,000 people, and the JW population assigned to a convention is...10-15,000! If there were 25,000 non-JW "public" suddenly clamoring to get in, where would they all sit? Plus, the talks are so loaded with Theocratese that Joe Public would have no idea what was being discussed.
This is strictly a "team-building" exercise. Unify the troops to do something different in field service, try to force a sense of "unity" in them.
It seems that maybe this will be more common, as there is another "special campaign" in September to hawk a "special edition" of the Awake magazine.