The big launch — the aggregator front pages, the large thread — is one shot each. Spend it before you can claim retention and you get the volume with none of the learning, and the card is gone.
The arithmetic is unkind. At a plausible early activation rate, two thousand signups and three hundred signups produce a similar number of retained accounts, because the constraint is the second week, not the first day. The two thousand cost a channel you cannot re-use and buried the signal in noise.
The unlock condition is a sentence, and stating it that way is what made this decision easy to hold under pressure: "X% of people who connect come back and capture in week two." When that sentence exists and is true, the launch has a story that lands. Until it does, the launch is an announcement that something exists.
Rejected alternative: launch small and quiet on the big channels to "test the message". That is not a test — those channels are winner-take-all within a day, and a soft attempt burns the slot at a discount.